Balak son of Zippor saw all that Israel had done to the Amorites.
Numbers Rabbah 20:2
What did he see? . . . It would have been better for the wicked if they had been blind, for their eyes bring evil on the world. In regard to the Generation of the Flood it is written, The sons of God saw (Gen. 6:2). It is also written, And Ham, the father of Canaan, saw (Gen. 9:22), and again it is written, And the princes of Pharaoh saw her (Gen. 12:15). It is the same with all the other cases, and it is the same here: And Balak saw.
Do we see the glass as half-empty or half-full?
The midrash suggests that it would be better for the wicked to be blind; that the very way in which they see the world brings evil on the world. The prooftexts give examples of people whose seeing led to disaster. If we change the thrust of the derash from "wicked" to "pessimists," I think we will understand the real point: that to walk through life seeing the glass as half-empty is not a way to walk through life at all. It would be better not to see, not to experience, not to live, than to constantly see only the negative, the wicked, around us. The way we see the world shapes our reality; seeing wickedness makes evil a reality.
Judaism is a fundamentally optimistic religion. Despite the challenges that have beset us as a people in every era; despite the difficulties we each experience in our own lives; we are to see the goodness in life, in people, in the world. A few chapters further, our parashah reads: "Then the Lord opened the eyes of Balaam" (Num. 22:31). There the midrash asks: "But had he been blind? No; it merely served to inform him that the eye also is in God's power" (Numbers Rabbah 20:15). Our eyes are vessels of holiness; we are to use them as instruments that see God's goodness in the world. We are to go through life not as wicked pessimists but as pious optimists, full of hope, and focus on all that is good. "Yet I have faith that I shall surely see Adonai's goodness in the land of the living. Hope in Adonai. Be strong, take courage, and hope in Adonai" (Ps. 27:15).