[chongli]

It's something that takes tons and tons of practice. The more positions and tactics and openings you burn into your long term memory the less you need to keep in short term memory.

The best players in the world have put so many thousands of hours into the game that they can beat casual players trivially without thinking more than one move ahead. They owe this ability to having vast knowledge of fundamentals and theoretical lines in all the most common positions. This is how they are able to win simultaneous exhibitions against a large number of casual players.