It's funny, a lot of us speculated that when Cooper finally returned, even before the Dougie stuff started, that he wouldn't be the same person just because he would've been tormented in the Black Lodge for 25 years, and that that torment would would fuck him up psychologically and, for instance, make him way less cheery than he used to be. But who figured that what Cooper was being tormented by all those years was not his own imprisonment, but his inability to save Laura, and that his escape from the Lodge wouldn't produce a more psychologically damaged person but instead a person more driven to change time and space in order to save Laura.