Waterfall vs. Agile: What’s Fixed, What’s Flexible, and Why It Matters
14 May 2025
BY SCOTT M. GRAFFIUS | ScottGraffius.com
Introduction
Not all project management approaches are created equal. This article explores how Waterfall and Agile differ in their treatment of scope, time, and resources—and examines the implications of those differences for project success.
This visual that heads up this article uses an apple and an orange to contrast Waterfall and Agile. It’s a simple yet powerful reminder that how a project is structured fundamentally shapes how it unfolds.
Read on for a closer look at how each approach handles the constraints and why the differences matter.
The Triple Constraint Triangle, Simplified
At the core of project management is the triple constraint:
Every project involves these elements, but how they’re prioritized depends on the approach.
Waterfall: Fixed Scope, Estimated (Flexible) Time and Resources
With Waterfall, the scope is locked in upfront. Teams then estimate how long it will take and what resources will be required to get it done. This structured, plan-driven approach assumes that what you're building is well understood from the start.
Waterfall works best when:
🔑 Key point: Waterfall fixes scope and adjusts time and resources to meet it. It offers predictability but limited flexibility.
Agile: Fixed Time and Resources, Estimated (Flexible) Scope
In contrast, Agile fixes time (e.g., sprint length) and team composition. The scope, however, is treated as adaptable, evolving based on feedback, priorities, and progress.
Agile excels when:
🔑 Key point: Agile adapts scope within a fixed delivery rhythm. It emphasizes responsiveness and collaboration over rigid planning.
Why This Distinction Matters
Understanding which variables are fixed versus flexible isn’t just a planning detail—it directly shapes how a project unfolds. Misaligning the approach with the nature of the work can lead to missed deadlines, wasted resources, and frustrated stakeholders. But when teams intentionally align their approach—fixing the right things and flexing the rest—they set clear expectations, reduce risk, and dramatically improve the odds of success. That’s why it matters.
Conclusion
Whether building a rocket or reimagining a product, understanding how the approach manages constraints is crucial. The right fit can mean the difference between momentum and mayhem. Projects can be complex. But understanding key differences between Waterfall and Agile can be as simple as comparing an apple to an orange (as depicted in Graffius' visual above).
More on Agile
Even More
Read on for…
About Scott M. Graffius
Scott M. Graffius is an AI, Agile, and Project Management/PMO leader, researcher, author, and speaker. Along the way, he spearheaded initiatives that have generated over $2.3 billion in impact for organizations across tech, entertainment, finance, healthcare, and beyond. The following sections provide additional information on his experience, contributions, and influence.
Experience
Graffius heads the professional services firm Exceptional PPM and PMO Solutions, along with its subsidiary Exceptional Agility. These consultancies offer strategic and tactical advisory, training, embedded expertise, and consulting services to the public, private, and government sectors. They help organizations enhance their capabilities and results in agile, project management, program management, portfolio management, and PMO leadership, supporting innovation and driving competitive advantage. The consultancies confidently back services with a Delighted Client Guarantee™.
Graffius is a former VP of project management with a publicly traded provider of diverse consumer products and services over the Internet. Before that, he ran and supervised the delivery of projects and programs in public and private organizations with businesses ranging from e-commerce to advanced technology products and services, retail, manufacturing, entertainment, and more.
He has experience with consumer, business, reseller, government, and international markets.
Award-Winning Author
Graffius has authored three books.
International Public Speaker
Organizations worldwide engage Graffius to present on tech (including AI), Agile, project management, program management, portfolio management, and PMO leadership. He crafts and delivers unique and compelling talks and workshops. To date, Graffius has conducted 93 sessions across 25 countries. Select examples of events include Agile Trends Gov, BSides (Newcastle Upon Tyne), Conf42 Quantum Computing, DevDays Europe, DevOps Institute, DevOpsDays (Geneva), Frug’Agile, IEEE, Microsoft, Scottish Summit, Scrum Alliance RSG (Nepal), Techstars, and W Love Games International Video Game Development Conference (Helsinki), and more.
With an average rating of 4.81 (on a scale of 1-5), sessions are highly valued.
The speaker engagement request form is here.
Thought Leadership and Influence
Prominent businesses, professional associations, government agencies, and universities have showcased Graffius and his contributions—spanning his books, talks, workshops, and beyond. Select examples include:
Graffius has played a key role in the Project Management Institute (PMI) in developing professional standards. He was a member of multiple teams that authored, reviewed, and produced:
Additional details are here.
He was also a subject matter expert reviewer of content for the PMI’s Congress. Beyond the PMI, Graffius also served as a member of the review team for two of the Scrum Alliance’s Global Scrum Gatherings.
Acclaimed Authority on Teamwork Tradecraft
Graffius is a renowned authority on teamwork tradecraft. Informed by the research of Bruce W. Tuckman and Mary Ann C. Jensen, over 100 subsequent studies, and Graffius' first-hand professional experience with, and analysis of, team leadership and performance, Graffius created his 'Phases of Team Development' as a unique perspective and visual conveying the five phases of team development. First introduced in 2008 and periodically updated, his work provides a diagnostic and strategic guide for navigating team dynamics. It provides actionable insights for leaders across industries to develop high-performance teams. Its adoption by esteemed organizations such as Yale University, IEEE, Cisco, Microsoft, Ford, Oracle, Broadcom, the U.S. National Park Service, and the Journal of Neurosurgery, among others, highlights its utility and value, solidifying its status as an indispensable resource for elevating team performance and driving organizational excellence.
The 2025 edition of Graffius' "Phases of Team Development" intellectual property is here.
Expert on Temporal Dynamics on Social Media Platforms
Graffius is also an authority on temporal dynamics on social media platforms. His 'Lifespan (Half-Life) of Social Media Posts' research—first published in 2018 and updated annually—delivers a precise quantitative analysis of post longevity across digital platforms, utilizing advanced statistical techniques to determine mean half-life with precision. It establishes a solid empirical base, effectively highlighting the ephemeral nature of content within social media ecosystems. Referenced and applied by leading entities such as the Center for Direct Marketing, Fast Company, GoDaddy, Pinterest Inc., and PNAS, among others, his research exemplifies methodological rigor and sustained significance in the field of digital informatics.
The 2025 edition of Graffius "Lifespan (Half-Life) of Social Media Posts" research is here.
Education and Professional Certifications
Graffius has a bachelor’s degree in psychology with a focus in Human Factors. He holds eight professional certifications:
He is an active member of the Scrum Alliance, the Project Management Institute (PMI), and the Institute of Electrical and Electronics Engineers (IEEE).
Advancing AI, Agile, and Project/PMO Management
Scott M. Graffius continues to advance the fields of AI, Agile, and Project/PMO Management through his leadership, research, writing, and real-world impact. Businesses and other organizations leverage Graffius’ insights to drive their success.
Thought Leader | Public Speaker | Agile Protocol Book | Agile Scrum Book | Agile Transformation Book | Blog | Photo | X | LinkedIn | Email
How to Cite This Article
Graffius, Scott M. (2025, May 14). Waterfall vs. Agile: What’s Fixed, What’s Flexible, and Why It Matters. Available at: https://scottgraffius.com/blog/files/waterfall-vs-agile-what-is-fixed-and-what-is-flexible-and-why-it-matters.html.
Digital Object Identifier (DOI)
DOI: (coming soon)
Content Acknowledgements
Names and marks are the property of their respective owners.
Copyright
Copyright © Scott M. Graffius. All rights reserved.
Content on this site—including text, images, videos, and data—may not be used for training or input into any artificial intelligence, machine learning, or automatized learning systems, or published, broadcast, rewritten, or redistributed without the express written permission of Scott M. Graffius.
Introduction
Not all project management approaches are created equal. This article explores how Waterfall and Agile differ in their treatment of scope, time, and resources—and examines the implications of those differences for project success.
This visual that heads up this article uses an apple and an orange to contrast Waterfall and Agile. It’s a simple yet powerful reminder that how a project is structured fundamentally shapes how it unfolds.
Read on for a closer look at how each approach handles the constraints and why the differences matter.
The Triple Constraint Triangle, Simplified
At the core of project management is the triple constraint:
- Scope – What are the project's objectives and deliverables?
- Time – What is the timeline for completion?
- Resources – What people/budget are allocated?
Every project involves these elements, but how they’re prioritized depends on the approach.
Waterfall: Fixed Scope, Estimated (Flexible) Time and Resources
With Waterfall, the scope is locked in upfront. Teams then estimate how long it will take and what resources will be required to get it done. This structured, plan-driven approach assumes that what you're building is well understood from the start.
Waterfall works best when:
- Requirements are stable and clearly defined.
- Upfront detailed planning is required (such as in construction or regulated industries).
- Changes later in the process are costly or risky.
🔑 Key point: Waterfall fixes scope and adjusts time and resources to meet it. It offers predictability but limited flexibility.
Agile: Fixed Time and Resources, Estimated (Flexible) Scope
In contrast, Agile fixes time (e.g., sprint length) and team composition. The scope, however, is treated as adaptable, evolving based on feedback, priorities, and progress.
Agile excels when:
- Requirements are unclear or are likely to change.
- Iteration and experimentation are critical.
- Value delivery needs to happen quickly and often.
🔑 Key point: Agile adapts scope within a fixed delivery rhythm. It emphasizes responsiveness and collaboration over rigid planning.
Why This Distinction Matters
Understanding which variables are fixed versus flexible isn’t just a planning detail—it directly shapes how a project unfolds. Misaligning the approach with the nature of the work can lead to missed deadlines, wasted resources, and frustrated stakeholders. But when teams intentionally align their approach—fixing the right things and flexing the rest—they set clear expectations, reduce risk, and dramatically improve the odds of success. That’s why it matters.
Conclusion
Whether building a rocket or reimagining a product, understanding how the approach manages constraints is crucial. The right fit can mean the difference between momentum and mayhem. Projects can be complex. But understanding key differences between Waterfall and Agile can be as simple as comparing an apple to an orange (as depicted in Graffius' visual above).
More on Agile
- The Agile's Journey Through the Decades article traces Agile’s fascinating evolution.
- The award-winning book Agile Scrum: Your Quick Start Guide with Step-by-Step Instructions helps readers implement and use the most popular agile framework―Scrum; deliver products in short cycles with rapid adaptation to change, fast time-to-market, and continuous improvement; and support innovation and drive competitive advantage.
- Thriving in today's marketplace frequently depends on making a transformation to become more agile. Those successful in the transition enjoy faster delivery speed and ROI, higher satisfaction, continuous improvement, and additional benefits. Based on actual events, Agile Transformation: A Brief Story of How an Entertainment Company Developed New Capabilities and Unlocked Business Agility to Thrive in an Era of Rapid Change book provides a quick (60-90 minute) read about a successful Agile transformation at a multinational entertainment and media conglomerate.
- Agile Protocol: The Transformation Ultimatum is an action-packed, darkly funny adventure that roasts Agile gone wrong—while also showing you how to get it right. This new book is the first Agile satire that blends hilarious corporate parody with actionable Agile insights!
Even More
Read on for…
- About Scott M. Graffius
- How to Cite This Article
- And more
About Scott M. Graffius
Scott M. Graffius is an AI, Agile, and Project Management/PMO leader, researcher, author, and speaker. Along the way, he spearheaded initiatives that have generated over $2.3 billion in impact for organizations across tech, entertainment, finance, healthcare, and beyond. The following sections provide additional information on his experience, contributions, and influence.
Experience
Graffius heads the professional services firm Exceptional PPM and PMO Solutions, along with its subsidiary Exceptional Agility. These consultancies offer strategic and tactical advisory, training, embedded expertise, and consulting services to the public, private, and government sectors. They help organizations enhance their capabilities and results in agile, project management, program management, portfolio management, and PMO leadership, supporting innovation and driving competitive advantage. The consultancies confidently back services with a Delighted Client Guarantee™.
Graffius is a former VP of project management with a publicly traded provider of diverse consumer products and services over the Internet. Before that, he ran and supervised the delivery of projects and programs in public and private organizations with businesses ranging from e-commerce to advanced technology products and services, retail, manufacturing, entertainment, and more.
He has experience with consumer, business, reseller, government, and international markets.
Award-Winning Author
Graffius has authored three books.
- Agile Scrum: Your Quick Start Guide with Step-by-Step Instructions, his first book, earned 17 awards.
- Agile Transformation: A Brief Story of How an Entertainment Company Developed New Capabilities and Unlocked Business Agility to Thrive in an Era of Rapid Change, his second book, was named one of the best Scrum books of all time by BookAuthority.
- Agile Protocol: The Transformation Ultimatum, his third book and his first work of fiction, was released in April 2025. The book trailer is on YouTube.
International Public Speaker
Organizations worldwide engage Graffius to present on tech (including AI), Agile, project management, program management, portfolio management, and PMO leadership. He crafts and delivers unique and compelling talks and workshops. To date, Graffius has conducted 93 sessions across 25 countries. Select examples of events include Agile Trends Gov, BSides (Newcastle Upon Tyne), Conf42 Quantum Computing, DevDays Europe, DevOps Institute, DevOpsDays (Geneva), Frug’Agile, IEEE, Microsoft, Scottish Summit, Scrum Alliance RSG (Nepal), Techstars, and W Love Games International Video Game Development Conference (Helsinki), and more.
With an average rating of 4.81 (on a scale of 1-5), sessions are highly valued.
The speaker engagement request form is here.
Thought Leadership and Influence
Prominent businesses, professional associations, government agencies, and universities have showcased Graffius and his contributions—spanning his books, talks, workshops, and beyond. Select examples include:
- Adobe,
- American Management Association,
- Amsterdam Public Health Research Institute,
- Bayer,
- BMC Software,
- Boston University,
- Broadcom,
- Cisco,
- Coburg University of Applied Sciences and Arts - Germany,
- Computer Weekly,
- Constructor University - Germany,
- Data Governance Success,
- Deimos Aerospace,
- DevOps Institute,
- Dropbox,
- EU's European Commission,
- Ford Motor Company,
- Gartner,
- GoDaddy,
- Harvard Medical School,
- Hasso Plattner Institute - Germany,
- IEEE,
- Innovation Project Management,
- Johns Hopkins University,
- Journal of Neurosurgery,
- Lam Research (Semiconductors),
- Leadership Worthy,
- Life Sciences Trainers and Educators Network,
- London South Bank University,
- Microsoft,
- NASSCOM,
- National Academy of Sciences,
- New Zealand Government,
- Oracle,
- Pinterest Inc.,
- Project Management Institute,
- Mary Raum (Professor of National Security Affairs, United States Naval War College),
- SANS Institute,
- SBG Neumark - Germany,
- Singapore Institute of Technology,
- Torrens University - Australia,
- TBS Switzerland,
- Tufts University,
- UC San Diego,
- UK Sports Institute,
- University of Galway - Ireland,
- US Department of Energy,
- US National Park Service,
- US Soccer,
- US Tennis Association,
- Verizon,
- Wrike,
- Yale University,
- and many others.
Graffius has played a key role in the Project Management Institute (PMI) in developing professional standards. He was a member of multiple teams that authored, reviewed, and produced:
- Practice Standard for Work Breakdown Structures—Second Edition.
- A Guide to the Project Management Body of Knowledge—Sixth Edition.
- The Standard for Program Management—Fourth Edition.
- The Practice Standard for Project Estimating—Second Edition.
Additional details are here.
He was also a subject matter expert reviewer of content for the PMI’s Congress. Beyond the PMI, Graffius also served as a member of the review team for two of the Scrum Alliance’s Global Scrum Gatherings.
Acclaimed Authority on Teamwork Tradecraft
Graffius is a renowned authority on teamwork tradecraft. Informed by the research of Bruce W. Tuckman and Mary Ann C. Jensen, over 100 subsequent studies, and Graffius' first-hand professional experience with, and analysis of, team leadership and performance, Graffius created his 'Phases of Team Development' as a unique perspective and visual conveying the five phases of team development. First introduced in 2008 and periodically updated, his work provides a diagnostic and strategic guide for navigating team dynamics. It provides actionable insights for leaders across industries to develop high-performance teams. Its adoption by esteemed organizations such as Yale University, IEEE, Cisco, Microsoft, Ford, Oracle, Broadcom, the U.S. National Park Service, and the Journal of Neurosurgery, among others, highlights its utility and value, solidifying its status as an indispensable resource for elevating team performance and driving organizational excellence.
The 2025 edition of Graffius' "Phases of Team Development" intellectual property is here.
Expert on Temporal Dynamics on Social Media Platforms
Graffius is also an authority on temporal dynamics on social media platforms. His 'Lifespan (Half-Life) of Social Media Posts' research—first published in 2018 and updated annually—delivers a precise quantitative analysis of post longevity across digital platforms, utilizing advanced statistical techniques to determine mean half-life with precision. It establishes a solid empirical base, effectively highlighting the ephemeral nature of content within social media ecosystems. Referenced and applied by leading entities such as the Center for Direct Marketing, Fast Company, GoDaddy, Pinterest Inc., and PNAS, among others, his research exemplifies methodological rigor and sustained significance in the field of digital informatics.
The 2025 edition of Graffius "Lifespan (Half-Life) of Social Media Posts" research is here.
Education and Professional Certifications
Graffius has a bachelor’s degree in psychology with a focus in Human Factors. He holds eight professional certifications:
- Certified SAFe 6 Agilist (SA),
- Certified Scrum Professional - ScrumMaster (CSP-SM),
- Certified Scrum Professional - Product Owner (CSP-PO),
- Certified ScrumMaster (CSM),
- Certified Scrum Product Owner (CSPO),
- Project Management Professional (PMP),
- Lean Six Sigma Green Belt (LSSGB), and
- IT Service Management Foundation (ITIL).
He is an active member of the Scrum Alliance, the Project Management Institute (PMI), and the Institute of Electrical and Electronics Engineers (IEEE).
Advancing AI, Agile, and Project/PMO Management
Scott M. Graffius continues to advance the fields of AI, Agile, and Project/PMO Management through his leadership, research, writing, and real-world impact. Businesses and other organizations leverage Graffius’ insights to drive their success.
Thought Leader | Public Speaker | Agile Protocol Book | Agile Scrum Book | Agile Transformation Book | Blog | Photo | X | LinkedIn | Email
How to Cite This Article
Graffius, Scott M. (2025, May 14). Waterfall vs. Agile: What’s Fixed, What’s Flexible, and Why It Matters. Available at: https://scottgraffius.com/blog/files/waterfall-vs-agile-what-is-fixed-and-what-is-flexible-and-why-it-matters.html.
Digital Object Identifier (DOI)
DOI: (coming soon)
Content Acknowledgements
Names and marks are the property of their respective owners.
Copyright
Copyright © Scott M. Graffius. All rights reserved.
Content on this site—including text, images, videos, and data—may not be used for training or input into any artificial intelligence, machine learning, or automatized learning systems, or published, broadcast, rewritten, or redistributed without the express written permission of Scott M. Graffius.