When Does Promise Turn To Stagnation?

Every year, one of the most interesting parts of the playoffs to monitor is this: who has room to grow, how do we give that to them, and when do we truly understand what a player is? We have those answers for players like Lebron James and Russell Westbrook. But what about the growth curve of younger players like Ja Morant, Karl Anthony-Towns, Trae Young, and Donovan Mitchell?