You are correct that pessimists are more prepared for negative effects, but are also more prone to negative occurances in a sense. Simply for the fact that they are expecting the worst and dont aspire to achieve the best.
So tell me, from the mouth of a pessimist, how do you react to a situation in which you expect the worst outcome, but instead receive the best? Do you continue to be pessimistic about the occurance or is there an aspect of optimism in a pessimists life? :P
Optimists that are unfortunate enough to persist through a raw deal and end up with the worst outcome will still, if strong hearted enough, look at the situation optimistically. A frequent quote of mine is :
'with every heart broken is a lesson learnt'
Sometimes it takes a great deal of emotional or phyisical pain for an individual to learn something (namely me) and with every sour situation i encounter and emerge through i always look back at it with a smile in knowing that i've become a more improved and better person because of it.
Again, it all comes down to the capability of yourself and your personal views :)