Hustle is a big part of defense. You must catch up to an offensive player who gets by you or pick up uncovered players going to the basket. Counterproductive Beliefs 10. So, off ball players always need to help out. Off ball players must be in position to rebound as well.
Defense is difficult to learn.
Defense is much easier to learn than offense. Not only is less skill involved, but there are also fewer skills to learn. You can't teach or learn hustle. It is one of the easiest, if not the easiest, skill to teach. All of the players I ever coached hustled.