chess is a game of combinatorics, the theoretical best move can be found by brute force scanning and calculation. computers are calculators. they have enormous amounts of memory and can calculate multiple lines each 50 moves ahead. a powerful computer can scan 120 million positions per second. my feeble psyche takes a at least a few seconds to calculate a line even just 2 moves deep. Most people’s short term memory can store 7 items so most people probably can’t calculate a single line further than that