personally I believe the most rational approach is to believe realistically and act optimistically. I believe whatever I think is most likely to be true, not what I want to be true. However in certain cases I may act as if what I wish were true is in fact true, just because it makes life better (doesn't apply to all scenarios though)
Why believe at all? What will happen will happen. If that's the end of civilization or a golden utopia will reveal itself in due time. Regardless, the way to act is the same, that is, true to yourself.
