People remember whether your confidence deserved theirs.

Every time you assert something confidently, you are making a small prediction that other people register. If it holds, your confidence becomes usable currency. If it fails, they remember not just that you were wrong but that you were sure, and they will discount the next assurance accordingly. Certainty is a claim on their trust that gets settled later.

Before you say you are sure, ask whether you would want this instance to be the one people remember. Reserve full confidence for the things you can defend. Being right about the things you were certain about is what makes certainty worth anything.