I think it's imperative. From an outsider's perspective, most start-ups look like a bunch of nuts riding the edge of sanity. From the inside, you have to convince yourself that you will succeed.
I'm not sure I've ever been that confident on a decent sized project. I'm starting to wonder if it explains a lot of things about me or if its just the latest convenient thing to tell myself :)
Yes, it looks a little bit like crazy.