The best paradoxes raise questions about what kinds of contradictions can occur—what species of… — William Poundstone

Are there any mythical beasts which aren't simple pastiches of nature? Centaurs, minotaurs, unicorns, griffons, chimeras, sphinxes, manticores, and the like don't speak well for the human imagination. None is as novel as a kangaroo or starfish.

At a bare minimum, understanding entails being able to detect an internal contradiction: a paradox.

The assumption that anything true is knowable is the grandfather of paradoxes.