Also attention. Lower level human players are more likely to make a move close to their own/their opponent's recent move. They're focused on one area of the board.

Basic computer opponents on the other hand can make moves all over the place. They look at the board state holistically. This can be very frustrating to play against as a human who has enough problems just thinking their way through some subset of the board, but is thrown off by the computer again and again.

It's not that bad in chess at least (compared to Go), but still something worth to keep in mind if you're trying to make an AI that is fun to play against as an amateur.