“Why” is the question that turns a rule into something you actually understand.

A rule you only know the shape of has to be remembered; a rule you understand can be rebuilt when you forget it. The reason also tells you where the rule stops applying, which is what separates following instructions from using them. Most rules exist because somebody hit a problem you have not hit yet.

Take one rule you follow without thinking, at school or on a shift, and find out what goes wrong without it. Ask, or look it up. The answer usually makes the rule much easier to keep.