Ethan Khoza explains why ball-handling drills don't work in real games: you never practiced against live defense. If you only do drills alone, you won't know how to dribble under pressure. Practice handling the ball in scrimmages and 1-on-1s instead.
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If you wonder why your handling doesn't transfer, it's probably because you don't know how to actually handle the ball when there's somebody trying to take it from you. You can do all the drills in the world, and I'm a fan of doing drills too, don't get me wrong. But you can do all the drills that you want to do. If you don't ever work on it against defense, you're never going to know how to actually apply it to games. And therefore it's never going to be something that actually shows up for you. You're going to spend all this time working on it and you're going to wonder why it's not transferring. You're not seeing the results in games, and it's because you haven't learned how to actually execute that skill. In the context of, hey, there's someone trying to take the ball from me one on with a friend, with a teammate, you can do it that way. It can also be a five on five game and you just try to handle the ball more or a three on three and you just, hey, my goal is to handle the ball more and to work on it this way. Force yourself to be a little bit uncomfortable sometimes, be willing to be uncomfortable and make mistakes until eventually you get better at it and it becomes something that you just can kind of do. You're always going to be limited if you do not work on handling the ball against actual defense. That's a really important thing.