What does it mean that pre-mortem as a calibration tool?

Imagining failure in advance corrects for optimistic perception biases.

Example: You're about to launch a new product feature. Instead of listing risks, you tell your team: 'It's six months from now and this feature has completely failed. Write down why.' Within ten minutes, a junior engineer surfaces a dependency risk that nobody mentioned in three weeks of planning meetings — because the prompt 'imagine it already failed' unlocked what 'what could go wrong?' never did.

Try this: Pick a decision or project you're currently planning. Set a timer for ten minutes. Write at the top of a page: 'It is [date six months from now]. This has failed completely.' Now write every reason you can think of for why it failed. Do not filter. Do not rank. Just generate. When the timer ends, review the list. Circle the two items that surprised you most — those are your calibration blind spots.