I prefer the term 'realist', however, I would say I'm definatly a pessimist.
Think about it:
If I'm wrong, that is a Good Thing(tm). I win.
If I'm right, I'm prepared for the worst. I win.
Therefore, I win 100% of the time.
The optimist just inflates his hopes for the best and don't put effort into fail-safe sollutions.
This might feel good, in a deterministic sort of way, but that feeling is the only positive thing about it, because when things fail, he's not prepared.