It's a coping mechanism. Personally, if I set my standards lower for this sort of thing then I have found I actually get over it much, much, MUCH quicker. And if I'm "wrong," hey, great! I'm just as pumped and thrilled and overjoyed as if I had been all bravado and cockiness, which definitely leaves me in a much worse mood for a while if things do go bad. I mean, I try to not just be a total Doom Boner (thought not always successfully) and more, like, "OK, here's how it seems like this COULD go wrong."