Certainty in a memory is not a sign of accuracy. Recollection is reconstructed each time it is used, and the sense of vividness attaches just as readily to details that were filled in as to those that were witnessed. People report things they are entirely sure of and entirely wrong about, without any dishonesty at any point.

Hold your own memories a little more loosely, especially in disputes where they matter. Ask what you actually saw as opposed to what you concluded. And extend the same allowance to someone who remembers an event differently, since they are as sure as you are and neither of you has a recording.