Just as when you mix pure and impure material, the result is impure, uncertainty can contaminate certainty but never the other way around. When you multiply an uncertain variable by a certain number, the result is uncertain and not certain. If the multiplier is >1, the result is even more uncertain this is leverage, which compounds uncertainty.So if you are told that a result is deterministic, say by theorem, but the person saying has a small probability of having made a mistake, the result will no longer be deterministic, but random.

(Cont, More technical) Unlike with water where bad elements get eventually diluted away, and where you can reach acceptable purity, if you add to N “well behaved” random variables (Mediocristan) a single “Extremely wild” one (super-Extremistan), the total sum will be “Extremely wild”, no matter how large the N or how well behaved the other random variables.
(The wild can be a single Cauchy-distributed random variable or anything with a tail exponent <=1).

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