Well, if they were to come on and read a post saying they might not be good enough Id hope at the very least, it would be something they are very aware of anyway, given the brutal competitive nature of professional football.
Also, if something so trivial was to effect the confidence that much then they certainly won't end up being good enough.
If I'd had just won a massive tournament and straight after people said to me 'yeah yeah well done but it doesn't mean anything. You might not make it', it would crush me now. Never if I was 16/17/18
Nonsense argument