It is wrong to call yourself a loser.
Janice is doing poorly in a diving competition and is preparing for her next dive.
Janice wants to say something to herself before her next dive.
Janice tells herself that she's capable of making a great dive and has done it successfuly hundreds of times before.
Janice tells herself that she's a loser for doing so poorly and that she's going to blow her next dive.
Janice is calm and focused and has her best dive of the competition.
Janice feels very dejected, expects to do poorly, and has her worst dive of the competition.