Module 9 · Planning & doing · Lesson 5 of 7

Realistic plans and the planning fallacy

We underestimate how long things take. Buffers, constraints and fewer commitments make plans survive.

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The idea

People reliably underestimate how long their own tasks will take — even when they know similar tasks ran late before. Psychologists call this the planning fallacy. We imagine the task going smoothly and forget the interruptions, delays and surprises that almost always happen.

Realistic plans correct for it. Look at how long similar things actually took last time, not how long you hope this will take. Add buffer time — extra space between tasks and before deadlines — for the things you cannot predict. Plan around constraints you know exist: work hours, family needs, your energy.

Overcommitment is the planning fallacy spread across a whole life: saying yes to more than your real hours can hold. A plan that fits your actual capacity, with room to breathe, is far more likely to be kept than an ambitious one that collapses by Wednesday.

Why it matters

Over-optimistic plans do more than run late. They create constant stress and a feeling of falling short, even when you are doing a lot. Realistic plans let you finish what you start and trust your own commitments again.

See it happen

Grace plans to redecorate her living room over one weekend: paint, new shelves and moving the furniture.

The first read

It is only one room, and she is organised, so a weekend seems like plenty of time.

With this idea

She remembers the bedroom took two weekends last year. She plans painting for this weekend, shelves for next weekend, and leaves Sunday afternoons free. It takes exactly that long, and she enjoys it instead of rushing.

What changed

She planned from how long things had actually taken, and added buffer.

Easy to get wrong

• Planning for the best case. Plan for the likely case, and let the best case be a pleasant surprise.
• Treating a buffer as wasted time. It is the space that keeps the rest of the plan intact.

Different perspectives

Reasonable people disagree here. None of these is presented as the final word.

Plan with past evidence

Research on the planning fallacy suggests using how long similar tasks actually took, rather than imagining this one, makes estimates far more accurate.

You will never fit everything in

Burkeman argues that the deeper answer is accepting finitude: no plan will hold everything, so the real skill is choosing what to leave out.

What this rests on

Well studied. Researchers have studied this a good deal. The core idea holds up, though details vary between people and settings.

• Roger Buehler, Dale Griffin & Michael Ross — the planning fallacy (1994) — Studies showing people underestimate how long their own tasks will take, even when they know similar tasks ran late before.
• Oliver Burkeman — Four Thousand Weeks (2021) — A book about time management that starts from finitude: you will never get everything done, so choosing is the whole skill.

Try it: Reality-check a plan

1. Take a plan you have for the coming week.
2. Next to each task, write how long a similar task actually took last time.
3. Add half as much again as a buffer, then see what no longer fits.
4. Decide what to move, shrink or drop.

Reflect

• Where are you consistently overcommitted?
• Which constraint do you usually plan as if it were not there?

Use it in the coming days

Plan next week on your schedule with buffers between tasks, and cut or move one commitment that no longer fits.

Where to do it: My Schedule

Your schedule shows plainly when a plan is bigger than the week.