The issue many young hitters have is that they don't understand that they need to be 'on time' twice on every pitch. They need to be 'on time' to move forward, and they need to be 'on time' to square the ball. If they fail to be 'on time' with their 'move out', then they will feel rushed and they will short-circuit their swing ... they will not be religious to their mechanics.
Just warning you in advance that I am stealing this line