Sin not to know – Netziv

Bamidbar (22:24) Balaam said to the messenger of G-d, “I sinned  because I did not know that you were standing in my way. If you still disapprove, I will turn back.”

Netziv (Bamidbar (22:24) I sinned because I didn’t know – Bilam’s main sin was his ignorance. He should have thought more carefully to understand what was happening to him