Gödel's Incompleteness Theorems

Two theorems in mathematical logic stating any system of logic and mathematics must be either incomplete, with questions it cannot answer, or inconsistent, giving contradictory or nonsensical answers in some situations.

In effect this means that no matter how advanced a system of logic (or the civilization that came up with it) is, something can always be learned from other systems. No one can know everything, which means it is useful to seek out alternate points of view in the form of alien minds.