τήν τε οἴησιν ἱερὰν νόσον ἔλεγε καὶ τὴν ὅρασιν ψεύδεσθαι
Heraclitus, fragment 46
Gnomic doesn’t begin to describe this one. Hmm. οἴησιν is translated variously as notion, opinion, conceit, arrogance, even as bigotry. The temptation is to amplify. ἱεραν νόσον is sacred disease or holy plague–which meant to the Greeks, epilepsy.
Opinion is a holy plague?…Conceit is epilepsy?…Bigotry is the sacred disease?…(Heraclitus) said, and seeing is deceiving.
I do think a self-regarding, strongly held notion or opinion could be considered a sort of epilepsy, in which case seeing is certainly deceiving, a kind of hallucination.