Start from the desired end state, or from how a plan would fail, and reason back to the actions required.
Attributed to Jacobi and popularised by Munger: invert, always invert. The premortem is its practical form, and it works because failure modes are easier to enumerate than success paths.
In practice
- A team designs a launch by asking what would have to be true for it to fail, then removing those conditions.
- A retirement plan built by starting from the desired income and working back is more tractable than one built forward from savings.