"Even though it was discovered by physicists, it's not a physical theory in the same sense as electromagnetism or general relativity. <...> Quantum mechanics is what you would inevitably come up with if you started from probability theory, and then said, let's try to generalize it so that the numbers we used to call "probabilities" can be negative numbers."

https://www.scottaaronson.com/democritus/lec9.html