The moment you’re totally sure is the moment you stop looking.

Certainty is efficient, which is precisely the problem. Once a question is closed, attention moves elsewhere and any evidence that would complicate the conclusion arrives to an empty room. Most of what people are wrong about for years is not something they never considered; it is something they settled early and never reopened. The feeling of being sure is a sensation, not a verification.

Take one belief you hold firmly and treat it as a live question for an hour. Look for the strongest case against it rather than the weakest. If it survives, you hold it better than before.