You know those days when you study really hard and all of a sudden, things just don't quite make sense anymore? It's that moment when your brain has officially given up and feels like a lump of goo.
This is the moment you're aiming for. Until you reach this moment, you probably aren't maximising your time or effort.
When you start learning a language, the goo-brain stage will probably come after an hour or so of poring over a grammar textbook. Later on, it may be a whole morning of grammar and an entire night of hanging out with native speaking friends before you reach this moment. But when it happens, relish it.