Answer: Conduct a “premortem” just before you decide to go ahead with an important decision.

Gary Klein, author of  Sources of Power: How People Make Decisions, thought up the premortem idea. He spells out why and how to do a premortem in this Harvard Business Review article:

Performing a Project Premortem

Daniel Kahneman glowingly describes the premortem technique in his book Thinking, Fast and Slow. He writes:

“The procedure is simple: When the organization has almost come to an important decision but has not formally committed itself, Klein proposes gathering for a brief session a group of individuals who are knowledgeable about the decision.

The premise of the session is a short speech:

‘Imagine that we are a year into the future. We implemented the plan as it now exists The outcome was a disaster. Please take 5 to 10 minutes to write a brief history of that disaster.’

Gary Klein’s idea of the premortem usually evokes immediate enthusiasm. After I described it casually at a session in Davos, someone behind me muttered, “It was worth coming to Davos just for this!” (I later noticed the speaker was the CEO of a major international corporation.)

The premortem has two main advantages: it overcomes the groupthink that affects many teams once a decision  appears to be made, and it unleashes the imagination of knowledgeable individuals in a much needed direction. . .The main virtue of the premortem is that is legitimizes doubts.  Furthermore, it encourages even supporters of the decision to search for possible threats that they had not considered earlier.” (p 264-5)

Kahneman again explains the technique  in this video–watch from 12 minutes 17 seconds: