Why Balak Believed Balaam's Blessing Took Heshbon From Moab

Midrash Aggadah, Numbers 22:6

"Curse for me this people" (Numbers 22:6) — like a man who picks the figs little by little. "Perhaps I shall be able to smite it" — like a man who subtracts from the measure little by little. "For I know that whom you bless is blessed" — because he had blessed Sihon and his people, and cursed the first king of Moab, so that by this means [Sihon] took Heshbon and his land from his hand, as far as the Arnon.

Biblical References