some single thing taht exists or occurs contradicts or diverges from an established theory or belief
Most societies, most western societies at least, generally go on the principle that "the exception proves the rule". WebC
“The familiar saying that the exception proves the rule contains a good deal of wisdom, though from the standpoint of formal logic it became an absurdity as soon as “prove” no longer meant “put on trial.” WebC
In each case, though, it seems like the exception proves the rule. WebC