I cant understand how thats not blatantly obvious.
only a small percentage of youngsters fulfull their potential. there is no way to say who will and who not, but right guidance helps alot.
For this reason, you dont just buy 3 and expect them to succeed. No, you buy alot more, have them have some healthy competition and learn from eachother, become better, and hope 1 or 2 break trough.
And dont be misled by "oh but barcelona does that"
No. they dont. They buy 20 players for each position EVERY YEAR, and once in a while one gets trough. the rest is sold and released.