Commit intelligently enough that second-guessing has to bring new evidence.

Commitment made with real thought earns a kind of protection. If you have already considered the objections, then a wave of doubt with nothing new in it can be recognized for what it is: anxiety rather than information. Setting that bar in advance is what keeps you from relitigating everything at three in the morning.

When you decide something significant, write down the reasoning and the main risks you accepted. Later, when doubt arrives, check whether it is bringing anything the note did not already contain. If not, keep going.