Is it because of their chess understanding? Or they just calculate and evaluate better than us? What the most important difference? Or are there many differences? CHess makes me so confused.
They have spent years memorizing and learning to calculate. They just are better at everything pretty much. Also I think most GM's have a particularly different style that gives some other subconscious level boost. Another subconscious advantage GM's have is extremely good intuition allowing them not to have to "calculate."
Plus they are very physically fit. You have to be to be able to focus and remember accurately for many hours. One glitch and your last 40 good moves are destroyed.