Expertise is invisible from inside

Somebody who has done a task for nine years has compressed hundreds of decisions into something that feels like a single move. Ask them how they do it and they will describe four steps. Watch them and there are nineteen.

The missing fifteen are not secrets. They are genuinely invisible to the person performing them — the glance at the account history before deciding, the one supplier whose invoices always need checking, the thing they do differently in the last week of the month.

Every one of those is a requirement. You will meet them all eventually; the only question is whether you meet them during a shadow day or during delivery.

Ask 'what made you do that?' every time

Whenever they do something you did not see coming, ask what prompted it. Not why — what made you. Why invites a justification; what made you invites a description of the trigger.

The answer is often "oh, because it was a Thursday" or "because that one came from Sarah". Those are business rules nobody has ever written down, and they are why the naive version of your system will be wrong 20% of the time.

Undocumented rules found in one day

How many decision rules you observed that nobody had mentioned in any conversation. Count them individually — this number is the best predictor you have of how wrong your first version will be.

From described to observed

The same task, as told to you and as performed. Then write one of your own.

Read the process back and be corrected

Write their process as you observed it and read it back to them. Not the owner — the person who does it.

They will correct you, and each correction is a requirement bought at conversation prices rather than delivery prices. They will also, frequently, be surprised by their own process written down.

The day you spent watching

One day of observation has just told you things a month of specification meetings would not have.