First mortise and tenon that fit like it meant it

Been fighting this joint for three weeks—swearing, shimming, re-cutting shoulders. Tonight it slid together with a soft thunk and I just stood there in the lamplight staring at it like an idiot. The master says it's not magic, it's repetition, but I'm not so sure. Feels like the wood finally decided to cooperate and it's the first time I get what he's been going on about.