Seeing the glass as half empty is more positive than seeing it as half full. Through such a lens the only choice is to pour more. That is righteous pessimism.
Confidence isn't optimism or pessimism, and it's not a character attribute. It's the expectation of a positive outcome.
Pessimism never won any battle.
Dwight D. Eisenhower
Positive thinking will let you do everything better than negative thinking will.