Why do i always get bad results when im confident/optimistic and vice versa?!?

Im sure no one has an explanation for this, but somehow...a mystic force does this to me. When i for example say that i 'Aced' a test, it doesnt turn out that way, while when i say 'it went bad', it sometimes happens i aced it. Ive always heard that confidence/optimism is good, but i dont know what to do cause i wanna score high! What do you guys think is better in life in general. optimism or the opposite. Doesnt being negative let you be more critical of things (look at the bad things) and allows u to correct them?