The Power Of Habit
I was recently playing some bullet chess with friends, and one of the onlookers made a comment about how impressed he was by how fast we could think, and calculate the moves. I smiled to myself because I knew the truth - the moves that were being churned out were more from memory, and years of playing than OTB (over the board) calculations.
When you've played the game for a while, certain things become second nature. You begin to unconsciously recognise patterns, schemes, and positions. Not only that, but you also know immediately how to react in certain situations without deliberate thought. This is however, something that you build up with time and playing loads of games.