Hold a pre-mortem before every major public project: “it failed — why?”

The problem: large projects regularly run over time and over budget, in part because of the planning fallacy, the tendency to underestimate the time, costs and risks of future actions while overestimating benefits.

The proposal: before approving a major project, hold a pre-mortem. Gather the people involved and ask them to imagine it is some years from now and the project has failed. Each person writes down the reasons independently, then they are pooled, grouped and ranked. The most serious risks get named owners, early warning signs and a plan.

Who acts: the project sponsor requires it; an outside facilitator, not the project's champion, runs the session; findings are included in the published business case.

Costs and trade-offs: a few hours of time. The risks are that it becomes a formality, or that critics are punished, so it works best when dissent is explicitly invited and protected.

First step: run a pre-mortem on the next project above a set budget threshold and publish the top five risks.