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

No chess engine is perfect. That is theoretically possible but way beyond the capabilities of any computer.

Each chess engine makes decisions by different means, using slightly different algorithms.