When a one-year project turns into three
Why we consistently underestimate how long things take, and what behavioural science can teach marketers, leaders and customer experience teams about setting better expectations.
When I started writing Customer Experience Thinking, I gave myself a year. It’s taken three. The book launches on 21st May 2026, which is a milestone I’m genuinely proud of. But getting here has thrown a spotlight on something I’d quietly been ignoring for most of the process: I am, by nature, wildly optimistic about how long things take.
Just me?
As it turns out, not even close. There’s a large body of evidence to reassure me that this is one of the most well-documented quirks of human thinking. It’s called the planning fallacy, and it doesn’t just affect personal projects. It shapes how teams work, how progress is perceived, and how customers experience the brands we build.
A bias as old as the modern study of bias itself
The planning fallacy was identified by Daniel Kahneman and Amos Tversky back in 1979. It’s the reliable, repeatable tendency we have to underestimate how long a task will take, how much it will cost, and how much risk it carries. Even when we’ve done the same task before. And even when the evidence is staring us in the face.
We plan for the best case. Reality delivers something else.
The reason is that when we estimate, we tend to look inwards. We picture the project going smoothly, we imagine the version of ourselves who’s focused and uninterrupted, and we build our timeline around that. Kahneman called this the “inside view”. It feels accurate because it’s specific and personal. But it ignores the one thing that would actually make our estimate more reliable, which is the messy, evidence-based history of every similar project we’ve ever done.
Why this matters far beyond project plans
This isn’t just a personal productivity issue. It shapes how teams work, how progress gets perceived, and how customers experience the brands we build.
If the people inside an organisation are consistently overestimating what they can deliver, three things tend to happen.
🧠Internally, teams feel like they’re falling behind on a daily basis, even when they’re working hard. That’s the productivity deficit, we can all relate to it, and it’s exhausting.
🧠Across departments, missed timelines compound. Marketing waits on product, product waits on tech, and the customer-facing team ends up apologising for a delay nobody owns.
🧠Externally, we set expectations with customers based on the best-case version of our plans. Then we miss them. And the gap between what we promised and what we delivered becomes the experience customers actually remember.
This is where the planning fallacy stops being a curiosity and starts being a customer experience issue.
The behavioural fix
The good news is that once you can identify and name a bias, you can design considering it. In the latest episode of The Customer Experience Lab, we get into the practical side of this in more detail, but here are the principles I keep coming back to:
✅ Use the outside view. Look at how long similar projects have actually taken in the past, not how long you hope this one will. The data is usually there, we just don’t like what it tells us.
✅ Set, manage and exceed expectations. This is the second of the 8 Customer Experience Principles, and the planning fallacy is one of the biggest reasons brands fail at it. Promise should be based on reality, not optimism.
✅ Build in the buffer publicly, not privately. Hidden contingency tends to evaporate. Visible, agreed contingency protects the team and the customer.
✅ Treat the timeline as part of the experience. A realistic deadline that’s met builds more trust than an ambitious one that slips. Every time.
🧠A thought for you
If something you’re working on is taking longer than you expected, it’s rarely a sign that you’re inefficient or undisciplined. More often, it’s our brains quietly setting an unrealistic baseline and then making us feel bad about not hitting it.
Understanding that doesn’t just help us plan better. It helps us design better experiences, for our teams and for our customers.
Hopefully, that’s a useful permission slip for anyone currently in the messy middle of something. Or at least an excuse that means my publisher won’t be too annoyed with me.
In this episode of The Customer Experience Lab , we look at rethinking the psychology of promotions.
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