"What distinguishes a Grandmaster from a master? Chess-lovers often ask questions like that. To many people it seems that Grandmasters simply calculate variations a little deeper. Or that they know their opening theory slightly better. But in fact the real difference is something else. You can pick out two essential qualities in which those with higher titles are superior to others: the ability to sense the critical moment in a game, and a finer understanding of various positional problems."
— Yusupov, in Opening Preparation