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?
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A lot of replies here are giving interesting facts about chess engines that don’t answer the question.
The ones that actually answer the question are a way down, talking about how randomness is built into algorithms, or computational details such as parallel processing and race conditions.
The answers at the top: fun fact, chess is really hard and even a computer doesn’t always know the best move! Yes, but OP isn’t asking why they don’t find the best move, they are asking why they don’t make the same move every time in the same situation. An algorithm can be imperfect but still deterministic, after all.
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