In this wonderful interview with physicist R.P. Feynman, he discusses the difference between thinking you know something, and actually KNOWING it. This discussion very much applies to almost any field of learning.
This post was inspired by a series of forum discussions I have recently been involved in. I am a firm believer that it is better to know less things well, than many things less deeply. Far too often students move on before truly getting the most out of a lesson.
Truly great players have learned to dig deeper into concepts. We should all follow that lead.