Sometimes it's just not about how much talent someone has or how much you think they can help you, sometimes time is what's needed.
Imagine you have an 8 year old kid and you're teaching him how to use a gun. He shows promise, he's actually a damn good shot, but he's too immature and not being responsible with the weapon (pointing it at people's heads, etc). The first couple of times you give him a stern warning, but if he's still not getting it you simply take the tool away until such time you think he's ready to be responsible.
Doesn't mean you've given up on him, doesn't mean he's "not your kind of kid", doesn't mean he can't help you win a tournament, it just means he needs time to process without the weapon in his hands, and you're not going to jeopardize everyone's safety before then.
Meanwhile, other kids who are worse shots (and make mistakes too) still get to participate because they're acting responsibly.