How do I make a big decision I can't easily undo?

Selling a business. Moving the family. Taking on a partner. Leaving a job. Some decisions are hard to reverse, and the pressure to get them right can make you stall, or rush.

Three simple tools help. None of them takes more than half an hour.

1. Imagine it already failed

Psychologist Gary Klein calls this a "premortem." Before you commit, picture this: it is a year from now, and the decision went badly. Now write down every reason why.

It works because of how our minds handle certainty. Klein points to a 1989 study in which imagining that an event had already happened, rather than that it only might happen, raised people's ability to come up with reasons for it by about 30%. Pretending the failure is real makes it easier to see what could cause it.

Take your list and ask of each reason: can I make this less likely, or can I live with it if it happens?

2. Write down what you decided, and how sure you were

Before you act, write a few lines:

• What you decided.
• The two or three reasons that mattered most.
• How sure you are, as a number out of 10.
• The date you will look back and check.

This takes five minutes, and it protects you from your own memory. Months later, we tend to remember being more certain than we were, and we rewrite our reasons to fit what happened.

3. Check how it turned out, and how you decided

Former professional poker player Annie Duke calls the habit of grading a decision only by its result "resulting." A good decision can turn out badly because of luck. A careless one can turn out well. If you only look at results, you learn the wrong lessons.

When the check-in date comes, ask two questions, and keep the answers side by side:

1. What happened, and how much of it was in my control?
2. Was the decision sound, given what I knew then?

Over time, your notes show you something no one else can: where your judgment is strong, and where you are often too sure.

The short answer

For a big decision you cannot easily undo: imagine it already failed and list why, write down your decision and how sure you are, then on a set date, check how it turned out and what that says about how you decided. Each decision teaches you something for the next.