If a young tennis player hasn't proved himself he won't make major tournaments. The focus and maturity is way above your average young footballer, because he plays alone he can't hide behind other players who can carry him in a game. Harvey Barnes is the equivalent of a young tennis player you actually get to hear about. I have noticed this for a while now, that an 18 year old footballer is still a kid. An 18 year old tennis player is a man because he has to be. These tennis players can't afford to get sloshed at night clubs, they are training 24/7. Hence the focus. Mentality HAS to be a major training essential for young "potentials" to be the real deal. You earn your first team place, it's not just a "try out" unless the match really doesn't matter.