I don't know if this will mean anything to you, but there is evidence that optimism can cause problems. (Admiral Stockdale was in a Vietnamese prison camp for many years, and noted that the most optimistic of the prisoners often didn't do well in captivity).

The Stoics practiced a type of negative visualization, where they would imagine the worst outcomes, up to and including the death of their beloved children. But, they did it so they could appreciate their children while they did live.