The light comes on when you stop thinking all together and just react, good stance, bad stance, grip etc.
I use the analogy of typing with students. Most of us can type and not think of all the things or brains are doing:
Master of the English language - or some where close
Understanding the alphabet and then scrambling all the letters on a key board.
Understanding of your computer and the systems/software etc.
I can type fairly quickly and accurately, until I think or look at the key board.
Another easier analogy is making a right turn in your car. When was the last time you planned it out and thought about every movement - Look, blinkers, feather gas, brake, gas brake, turn, look, gas, finish the turn smooth, etc...you get the picture.
Train with shooting the same way. Get to where drawing, sight picture, trigger press, follow through is one seamless thoughtless motion.