The negative thinkers can turn into over-achievers. Thinking that if they're really productive, they will get promoted.
Unfortunately for them, once they realize this is not the case, they get angry, frustrated, cynical.
Meanwhile the positive thinkers become high performers, who achieve less individually and in any given week and realize that working as a group and motivating people is more important than individual contributions. They stay in the game longer and turn into good leaders. They get promoted while the negative thinkers leave in search of the recognition they've earned but don't seem to get anywhere.