Chazal tell us that Korach was a wise man. If so, what caused him to rebel against Moshe and arouse so much negative sentiment among the people? On the Pasuk with which Moshe admonishes him and his followers, RAV LACHEM BNEI LEVI, “…you have taken too much, you sons of Levi” (Num. 16,7) Rashi comments: Korach who was a clever man what reason had he to commit this folly? Rashi answers: EINO HIT’ATO, “…his eye misled him…”. A person has two eyes. One can say homiletically a person should look with both eyes. With one he should recognize the greatness of Hashem and with the other he should recognize the lowly stature of man.
Korach saw with one eye. He recognized the greatness of Hashem. He stated that all the people are holy and among them is Hashem. He was a believer and was cognizant of Hashem’s greatness. However, he did not see with the other eye. He did not see his own position and thought he was more important than he truly was.
That is what Rashi meant when he said “his eye misled him”. He thought too highly of himself and thus acted foolishly.