Midday Feminist Work Rant

What is it about some men that gives them the power to make me doubt myself? I don't get it. In general, I'm a pretty confident person, who strongly believes in herself. Sometimes, though, I present an idea, expecting them to follow my lead, and walk away doubting myself . Just now, for example, I went to discuss an issue with a subconsultant, who should answer to me, as an architect. His response was that what I was saying couldn't possibly be true, and he argued with me for 10 minutes. Even though I had gotten the information from a trusted source, his response, his insistence that he was right, was enough to make me wonder if I was wrong. I recently got in a bit of trouble for arguing with this man, so I just walked away from the argument, but I knew I was right; I have back-up research to prove it. I hate, hate, HATE having to ask my boss or department head to solve this kind of issue for me! Why can't I just be confident enough to insist on my answer being correct?