" The best way to speed your learning is to avoid lazy learning. If you spend too much time on material you already know, you won’t have time to learn new material. This idea of focusing on the harder stuff is called deliberate practice.2 Deliberate practice is how you become an expert more quickly in whatever you are studying.3 "

― Barbara Oakley , Learning How to Learn: How to Succeed in School Without Spending All Your Time Studying; A Guide for Kids and Teens