How unvalidated assumptions lead capable teams to deliver late and over budget.

What Coherent Execution Looks Like

Most people have seen it, even if they don’t know what it’s called.

Huge flocks of starlings moving together in the sky – thousands of birds turning almost instantly, no leader, no shouting, no lag. It looks effortless, as if the flock were a single living thing rather than a mass of individuals.

People sometimes call it a murmuration, but the name doesn’t matter. What matters is what you’re seeing: a very large group moving together without hesitation or confusion. Nothing about starlings is especially clever. They don’t understand the shape they’re making or where the flock is ultimately heading.

What they do have is clarity.

Each bird knows the rules it must follow, which neighbours matter, and the pace at which the flock is moving. When something changes, the response is immediate. There is nothing to interpret and nothing to guess.

How Most Large Programs Actually Run

Now contrast that with how most large programs actually run.

Anyone who has spent time with children will remember watching them try to complete a jigsaw puzzle without the picture on the box. It can be done, eventually, but only with an extraordinary amount of luck.

Pieces get pushed together because they seem to fit. Progress looks convincing for a while, until it suddenly isn’t.

Frustration builds, confidence drains away, and, more often than not, the puzzle is left unfinished.

Large programs are run in much the same way. Not because people are careless or incompetent, but because we quietly ask hundreds – sometimes thousands – of capable people to guess how their work fits together.

They guess priorities, dependencies, timing, decision rights, acceptable risk, and whether it is safe to surface a problem early. When that happens at scale, programs don’t “fail” in a dramatic sense – they miss the mark.

Timelines slip. Costs creep. Scope erodes. Outcomes disappoint.

Why Guesswork Persists

This is why so many large programs miss their targets despite intense effort and deep experience. The problem is not a lack of intelligence, commitment, or process. It is that uncertainty is allowed to persist for far too long.

Under pressure, people do what humans naturally do. They protect their patch, manage impressions, delay bad news, optimise locally, and wait for permission. None of this is malicious. All of it is predictable. And all of it fragments execution.

Why the Starlings Matter

The starlings are useful here not as inspiration, but as contrast. Their behaviour works because guesswork has been removed.

Each bird knows what to pay attention to and how to respond. The system itself makes the right behaviour unavoidable, which is why the flock holds together even under threat.

When Structure Makes Guesswork Worse

Human organisations rarely create those conditions, especially large ones.

Most programs sit inside functional structures where accountability runs up and down silos, while the real work happens between them.

Dependencies stretch across organisational boundaries, forcing people to infer how their work fits with everyone else’s.

Even when cross-functional teams are formed, they are often left to self-organise without a clear sense of pace or priority. Some uncertainty is reduced, but much of it remains.

The Real Role of Leadership

This is where leadership really matters.

Coherent execution does not emerge by accident. Someone must set the pace and hold it. Leadership in complex programs is not primarily about motivation, vision, or oversight.

It is about removing guesswork so people can act with confidence.

A useful analogy is an orchestral conductor, properly understood. A conductor does not control the musicians or issue instructions mid-performance.

They establish tempo, interpret the score, surface imbalance, and insist on listening. Their authority comes from creating shared understanding. Without that, even the most talented orchestra falls apart.

Why Independent Program Reviews Matter

This is also why Independent Program Reviews matter – when they are done early and properly.

An IPR removes guesswork by making the implicit explicit, quickly. It surfaces assumptions, contradictions, ownership gaps, and unrealistic pacing before they harden into delays, overruns, and lost scope.

For leaders, this can be uncomfortable. It is also clarifying. Once guesswork is removed, the path forward is usually obvious.

If this feels uncomfortably familiar, it should.

The Part We Usually Avoid Saying Out Loud

Here is the part we usually avoid saying out loud.

If people are guessing in your program, that is not an execution problem – it is a leadership decision.

Ambiguity doesn’t persist by accident. It persists because no one has taken responsibility for removing it.

Large programs don’t miss the mark because they are uniquely complex.

They miss the mark because they are allowed to run on guesswork.

Guesswork, at scale, is not a risk.

It’s a pile-up of unvalidated assumptions – and tolerating them is a leadership decision.

About the author

David Hilliard is founder of Mentor, specialists in strategic program execution.

You can call him on 0118 359 2444 or email david.hilliard@mentoreurope.com.