That's really interesting because my partner always seems certain about everything! And sometimes something he will have expressed certainty about will turn out wrong. This used to ENRAGE me. He told me he feels certain and sure about these things - it's just that he turns out to have been mistaken about whatever it is. Even if I'm certain about something I often find it difficult to express with certainty. I'm always hyper-aware of how I might be wrong. At some points I have thought it might be a gender thing - boys are raised to be more certain about themselves - but to be honest I think it goes deeper...