When different chess engines play against each other, they don’t always have the same outcome. Why not?

Question

This has bugged me for a bit. If chess engines are meant to always play the best moves, then how come two chess engines playing against each other doesn’t always have the same winner?

In: Other

Answer 1

They dont always play the best move, they play what they think is the best move. The competition is there to find out which chess engine gets the closest to playing the best move more often than the other.