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 do have the same outcome if the AI plays 100% of the game. That’s why humans will force the white engine to use a variety of different openings. If they weren’t forced by humans to play a variety of openings, they would just open with the same opening every game.