A correct assumption is still weaker than a verified fact.

An assumption that turns out right was still a bet. You were not tracking the reasoning, you were tracking a guess that happened to land, and the same process will produce a wrong answer next time with exactly the same feeling of confidence. Being correct by luck teaches you nothing about when to trust yourself.

When a hunch turns out to be right, take a moment to ask what would have told you either way. Then, on the next thing that matters, spend the few minutes to check rather than assume. You are not doubting yourself, you are building a record of which of your instincts have earned their reputation.