Josh waitzkin breaks this down really well in his book the art of learning.

He's a chess champion and push hands champion and discusses how to learn. Basically as you become and expert in something you learn to pay less attention to the surrounding environment and only focus on what matters, which allows you to see it in "slow motion". This applies to chess champions where masters eye movement focuses on a much smaller part of the board than a beginner, and also in push hands or BJJ where experts fighting for a tiny bit of grip change is what matters but a novice might just see the whole body not moving or doing anything that matters.

Very worthwhile read.