On one level an unbiased expectation is optimal because it allows us to allocate our resources more efficiently. But there are many cases where this is not true, where a little too much hope and faith actually makes you a more successful person, and more fun to be around. Just think about how annoying ‘brutally frank’ people are–they are jerks. Think about the guy who thinks he is a better dancer than he really his confidence actually makes him a better dancer, because part of good dancing is not being self-conscious. Robert Trivers has pointed out that self-deception is, in moderation, an evolutionary advantage, in that a liar who believes his own lies is a more effective persuader than a lie who knows he is lying, and fundamentally we are social animals trying to convince others to do this or think that.
In fact, I contend that part of being good in anything lies in not being self-conscious. Self-consciousness is a kind of sucker. It eats up a lot of time and energy with no outcome, except for a dose of mental fatigue.