but it wasn't just that. we're shown earlier that he was spamming 'i want to be like him. i want to be like him. i want to be like him.'
the story is about a character tasting success and wanting it more than anything. he craves it. he needs it. and so in the beginning, when he cant have that and feels betrayed by someone who has everything- he's desperate. he's not thinking. he didn't have to kill himself 4000 times, but he... was never quite sane to begin with.
he killed someone who had everything he didn't, and he wanted that everything for himself. he's not completely sane. a sane person would have stopped at the lottery winning. he wants to be the best, so he eliminated the person that was standing in his way. it wasn't even all about him being evil. it's that, but other things too.

Realistically though, would someone really be able to kill themselves over 4000 times without any hesitation between each deaths? despite all the pain? and is perfectly sane after?