Every executive running project-driven work has been in the room where planning happened. Requirements got documented. Schedules got built. Resource plans got mapped. Sponsors signed off. Everyone left the room thinking they had a solid plan.
And then the project came in over budget. Or under scope. Or missed the deadline. Or produced something that solved a different problem than the one leadership actually needed solved.
Nobody skipped the planning phase. So what actually went wrong?
The data most executives haven’t seen together
The scale of the problem is easier to ignore when you look at individual project overruns instead of the aggregate pattern. Recent research makes the aggregate hard to unsee.
Bent Flyvbjerg’s 2023 analysis of more than 16,000 large IT projects found they run an average of 73% over budget. 18% of them exceed their budget by more than 50%, and those overrun by an average of 447%. Projects at that scale effectively become entirely different, far more expensive projects than what leadership approved.
The Standish Group’s 2020 CHAOS research shows only 31% of software projects succeed on time, on budget, and with full scope. 69% end up challenged or failed outright. Wellingtone’s 2026 State of Project Management Report found that only 36% of organisations complete projects on time always or most of the time. PMI’s 2020 Pulse of the Profession put the cost of getting this wrong at 11.4% of every dollar invested in projects, wasted on poor performance.
This isn’t a technology problem. The software works. The vendors deliver. The teams do their jobs. The plans were built on assumptions and requirements that didn’t match what the business actually needed, and the projects executed faithfully against the wrong targets.
The IT research is where the largest datasets exist because IT projects have the most consistent cost and schedule tracking. But the underlying failure patterns show up across every industry where projects span multiple functions. Engineering programs. Manufacturing rollouts. R&D initiatives with commercial dependencies. Anything where the plan gets built by one group and executed by another.
The reframe: five project planning mistakes
Companies aren’t failing at delivery because they didn’t plan. They planned. They spent hours in planning meetings. They produced documents. They aligned on schedules.
They failed because of how they planned. Five project planning mistakes keep showing up across the industries we work in most closely: technology, engineering, manufacturing, and cross-functional programs that touch all three. It is the same reason a new tool rarely fixes broken delivery: the problem was decided before execution started.
Pattern 1: Speeding through planning with assumptions
The urgency to get to execution eats the time planning actually needs.
Somebody’s calendar is already dependent on the launch date. The board committed to the outcome at last quarter’s review. The vendor’s proposal came in tighter than the internal team wanted, and nobody wants to be the one to say the timeline needs to slip before it even starts.
So planning gets compressed. Assumptions get made about vendor delivery reliability, internal resource availability, integration complexity, stakeholder response times. Nobody validates the assumptions. They get written into the plan as if they were confirmed.
Then reality diverges from the plan within the first few weeks. The vendor takes longer than assumed. The internal resources have competing priorities that weren’t surfaced. The integration turns out to be harder than the estimate. Every one of those was knowable at planning time. Nobody had time to actually check.
Pattern 2: Wrong people in the room at planning
The people who will actually do the work often weren’t in the room when the plan got built.
Sponsors were there. Vendor account teams were there. PMO leaders were there. Sometimes a director or two. What’s missing: the engineers, PMs, developers, or operators who have to execute against the plan and know what execution actually costs.
The plan then reflects what leadership hopes will happen. Not what the people doing the work know is possible. When execution begins and the workarounds start on day one, that gap is the reason.
Pattern 3: No lessons learned from previous projects
Every organization has a track record. Which vendors are always two weeks late. Which internal groups need double the ramp-up time they’re given. Which integration points have failed on the last three projects. Which sponsors change their mind halfway through and force replanning.
Almost nobody reads their own project post-mortems before planning the next project. The lessons are documented. They’re sitting in a shared drive somewhere. But planning meetings for the next project start from a blank template instead of from what the organization has already learned.
The result is that the same failure patterns get planned into the schedule. A vendor that has been late on every recent engagement still gets an aggressive timeline because the plan doesn’t account for their actual track record. The same requirements-drift problem that killed the last three projects doesn’t get a mitigation strategy because nobody remembered to look.
Pattern 4: Cross-functional silos at planning
This is where the biggest overruns happen. And it’s the failure pattern most concentrated in industries where projects cross functional boundaries.
R&D plans their piece. Engineering plans their piece. Manufacturing plans their piece. Each group builds a schedule that’s internally coherent. Nobody plans the seams between them.
Then the actual project spans all three functions, and each group assumes the other groups did their part. R&D hands off to engineering assuming certain specifications are locked. Engineering hands off to manufacturing assuming certain tolerances have been validated. Manufacturing ships assuming certain quality gates have been passed.
When the seams fail, nobody owns them. R&D says engineering should have caught it. Engineering says R&D should have specified it. Manufacturing says both of you should have told me. The finger-pointing begins, weeks get lost, and the timeline that everyone agreed to at planning becomes impossible to hit.
The seams between functions are where planning has to do the most work. In most organizations, they’re where planning does the least. That gap is also where project margin goes.
Pattern 5: Communication assumptions downstream
Planning meetings end. Everyone in the room leaves with what they think is a shared understanding of what got decided.
But the assumptions each function made about the others were rarely written down. What R&D committed to deliver by a specific date was based on assumptions about what engineering needed. What engineering committed to was based on assumptions about what manufacturing could accept. None of those assumptions got documented as assumptions.
Weeks later, when work needs to hand off, each group discovers the others had a different picture of what shared understanding meant. Delays compound. Rework starts. The project that was supposed to run cleanly from planning to launch is now running from crisis to crisis.
What good planning actually looks like
None of these failure patterns are unfixable. What they require is deliberate design, not more planning meetings.
- Validated assumptions instead of accepted ones. Every assumption in the plan gets a validation owner. Vendor timelines get checked against their actual track record on similar work. Resource availability gets confirmed with the resource owner, not assumed from a project management tool.
- Execution-level people in the planning room. The engineers, PMs, developers, or operators who will do the work are in the room when the plan gets built. Not to slow things down. To catch the things leadership can’t see from where they sit.
- Post-mortems consulted before schedules get built. Every planning session starts with a review of the last three relevant post-mortems. What went wrong. What patterns showed up. What we learned. Then plan against what we know, not against what we hope.
- Cross-functional seams planned explicitly. When a project spans multiple functions, the seams between them get their own planning workstream. Who owns what at each handoff. What quality gates have to pass. What escalation paths exist when the handoff isn’t clean.
- Communication protocols documented at the start, not improvised at the crisis point. Every assumption each function made about the others gets written down as an assumption. Regular checkpoints validate whether the assumptions are still true.
The organizations that face this squarely are the ones whose next project actually lands
Planning failures aren’t glamorous. Nobody wants to admit that their multi-million-dollar overrun started in a planning room where everyone thought they were being efficient.
But that’s where most of them start. Not in execution. Not in technology. Not in the vendor. In the way the plan itself got built.
The organizations that face that squarely are the ones whose next project actually lands.
Recognizing any of these patterns in your own delivery?
EPMA works with executives running project-driven operations to design planning approaches that catch these failure patterns before they become budget overruns.
If your projects keep coming in over budget or under scope even though everyone signed off on the plan, that’s the conversation we’re built for.
Frequently Asked Questions
Why do most large projects fail?
Most large projects fail because of how they were planned, not because planning was skipped. Bent Flyvbjerg’s 2023 analysis of more than 16,000 large IT projects found average budget overruns of 73%, with 18% of projects exceeding budget by more than 50% and those overrunning by an average of 447%. The Standish Group’s 2020 CHAOS research shows only 31% of software projects succeed on time, on budget, and with full scope. Plans got built on assumptions that didn’t hold, and everything downstream inherited the error.
Is project failure really that common?
Yes, at meaningful scale. Wellingtone’s 2026 State of Project Management Report found only 36% of organisations complete projects on time always or most of the time. Standish’s 2020 CHAOS research puts 69% of software projects in the challenged or failed categories. PMI’s 2020 Pulse of the Profession found 11.4% of every dollar invested in projects is wasted on poor performance. Most executives running project-driven operations have personally lived through several overruns of 20 to 50%.
What are the most common project planning mistakes?
Five patterns show up most often across technology, engineering, manufacturing, and cross-functional programs: speeding through planning with unvalidated assumptions, excluding execution-level people from the planning room, ignoring lessons learned from previous projects, failing to plan the seams between functions on cross-functional work, and not documenting the assumptions each group made about the others during planning.
Isn’t this just an IT problem?
No. The published research is IT-focused because IT projects have the most consistent data collection around cost and schedule outcomes. But the underlying failure patterns show up in every industry where projects span multiple functions. Engineering programs, manufacturing rollouts, R&D initiatives, and cross-functional programs with multiple handoff points all show the same planning-failure signatures.
How do we know if our planning process has these problems?
Look at your own recent project post-mortems. If the same failure patterns appear across multiple projects (vendor delays that weren’t planned for, requirements changes late in execution, handoff failures between functional groups), your planning process is the pattern. Also examine who was actually in the planning room versus who did the work. If the two groups don’t overlap significantly, that’s a leading indicator.
What’s the highest-leverage change we can make to project planning?
Two moves consistently produce the biggest reduction in project overruns: putting execution-level people in the planning room from the start, and explicitly planning the seams between functions on cross-functional projects. Both require deliberate design of who’s in the room and what gets documented, not more planning meetings.
EPMA is a project management consulting, staffing, and technology firm serving executives, PMO leaders, and mid-market operations leaders across energy, infrastructure, engineering and manufacturing, technology, and professional services. With over 17 years of history in project and portfolio management, EPMA helps clients design governance, measurement, and delivery infrastructure that turns strategy into provable business outcomes.
Sources
Bent Flyvbjerg and Dan Gardner, How Big Things Get Done (2023), base rates from a database of 16,000+ projects
The Standish Group, CHAOS 2020 (software project success, challenged, and failed rates; full report is paywalled)
Wellingtone, The State of Project Management Annual Report 2026 (March 2026)
Project Management Institute, Pulse of the Profession 2020 (11.4% of investment wasted due to poor project performance)