A very idealistic interpretation of the Pokemon universe. Pokemon really enjoy fighting and are never seriously injured, just really tired, and they like having trainers for the same reason athletes like having coaches and cheerleaders. They're about as smart as dogs so it's pretty easy to tell when they're happy with something.
Trainers tend to buy into the show's ethos of "being good at Pokemon comes from Friendship and Teamwork and Trying Hard Together and Having a Strong Bond", and they're generally right.