I don't think there is anything necessarily "wrong" with being a more "realistic" thinker, or a more optimistic one. Some people are just more naturally pessimistic, while others are naturally more positive in their thinking.

As long as one doesn't take it to the extreme (for pessimistic, thinking EVERYTHING will go wrong, and for optimistic, thinking EVERYTHING will be perfect and there's no way anything bad could happen), then you are just fine! There is definitely a benefit to being realistic.