>Wild Pokémon tend to be jealous of human-trained Pokémon.

This is said the in the first episode of the anime. But does this also make sense for the world of the mainline games? Yes, I think it does. It's easy to be all:
>Pokémon are SLAVES who are FORCED to fight and SHOVED into tiny metal balls!
But that's just stupid when you spend even a few minutes to think. Being a Wild Pokémon sounds like it would be a miserable existence of constantly trying to survive. You could be in actual danger, be seriously injured or even die instead of simply fainting and that's if we ignore Pokédex Entries. Compare that to a Trainer's Pokémon who are cared for, have their needs met and achieve many things that they never could have on their own.

I could see many Wild Pokémon seeing the kind of life a Trainer's Pokémon lives and thinking:
>I wish that was me...