Pre-mortem

Imagining, before committing, that the decision has failed badly, and writing down why.

The technique works because it changes the question from whether this could go wrong, which invites a defensive answer, to why it did go wrong, which invites specifics.

Applied to an investment it produces a list of the two or three things that would actually destroy the thesis, which is also the monitoring list for the position.

Fifteen minutes, in advance, and it changes the position size more often than not.