I said nothing about practicing "hard". Some players look good going through drills, some even look good in 5 on 5, but they have a tough time translating it to game action. On the other hand you've got some players that practice hard but just don't look that great in drills but in live game situations they have the intangibles that help the team win.
One famous NBA coach used to say if he needed someone to hit a shot to win a game he would pick Michael Jordan. But if he needed a player to hit a shot to save his life he would pick Larry Bird. Some people are just more reliable when the pressure is on.