A new study shows that people who are pessimists are to live a longer and healthier life than the ones who see sunny days even when in the middle of the wildest storm. 
I always wondered why humans are allowed to be pessimistic in the first place.
Why would Nature allow us to think badly for the future? After all, why not fool yourself that everything will go OK? Either way, what will happen will happen. Or do we really think we can alter the flow of the Universe?
At the end, life seems to be pessimistic it self. Death is its final destination. How stupid must you to be optimistic?