If a subject gets easy, add a harder layer. Coasting feels like mastery right up until it doesn’t.

Comfort in a subject is a sign you have stopped growing in it, not that you have finished. Coasting feels exactly like mastery because both are effortless, and the difference only surfaces when something slightly unfamiliar arrives and the floor turns out to be lower than you thought. Difficulty was the part doing the teaching.

When something starts feeling easy, go and find the harder version yourself. The next chapter, the extension questions, the drill at full speed. Staying slightly out of your depth is the whole method.