Pessimist

Generally, I think in most cases we all should be a bit pessimistic. Being objective is hard and personally I'd rather have a nice surprise than a great disappointment. But that's arguable - I guess optimistic people live longer - but then again, the benefit of long life is arguable as well.

But what I think is not really arguable, is that in my line of work you have to be pessimistic. A major part of being a sysadmin is keeping the system stable, and you can't really do this by being optimistic. To make the system stable you try to think about any scenario as improbable(and pessimistic) as it might be. One good example I can think of, is that having a daily backup is very important in our organization(and I really do hope we're not the only ones), yet for most systems, we've never needed those backups.

I might be taking this a bit too far when I'm berating team members who behave "too optimistically" and tend too answer "I'm getting paid for it" when asked why I'm so pessimistic, but I'm really just trying to make my point.