Beverages & Psychology?

Optimism is good and pessimism is bad. This is what we are taught from the very earliest stages on. We are reminded not to act as though the glass is half-empty but as though it is half-full. But I think both optimism and pessimism are good, and I think both optimism and pessimism are bad.
The standard argument is that the way we perceive events has a direct effect on the outcomes of those events. This is true in some respects, but I have yet to meet an optimist who has everything work out perfectly for them. Alternatively, I have yet to meet a pessimist who has never had anything work out for them.
Optimism certainly has it's advantages, but so does pessimism. If you go through life always expecting the worst, then you will go through life always prepared for the worst. This mirrors the disadvantage of optimism which is that if you go through life expecting only the best, then you will not know how to react when reality happens and something goes wrong. I may sound like a pessimist saying that reality means something going wrong, but I am not. If nothing went wrong in real life, then how would we know what is right?
Optimism and pessimism should both be taken in moderation. I prefer to play them against each other and approach things with indifference. That way, you are not disappointed when things go horribly wrong, and you are pleasantly surprised when things go perfectly.