Can someone explain this line to me: "As I had early discovered in school wherein I had excelled without labor, guided by theory, while many others, without ma

Can someone explain this line to me: "As I had early discovered in school wherein I had excelled without labor, guided by theory, while many others, without mastery of theory, failed despite monstrous effort." Is he talking about conceptual understanding vs rote memorization? What theory is he talking about?