Spaced repetition recap Mastering any subject is built on a foundation of knowledge: knowledge of facts, of heuristics, or of problem-solving tactics. If a subject is part of your full-time job, then you’ll likely master it through repeated exposure to this knowledge. But for something you’re working on part-time—like myself learning Japanese—it’s very difficult to get that level of practice. The same goes for subjects in school: a few hours of class or homework a week is rarely enough to build ...