You remember the story. It is found in Numbers 13.
The Israelites are camped in the wilderness. The Promised Land, Canaan, is just to the north. Their long journey from Egypt promises to be nearing an end.
God tells Moses to select a representative from each of the twelve tribes, men who would enter the Land for the purposes of looking it over and confirming to the nation that it was indeed the land of blessing God had proclaimed it to be. God is clear: the Land will be given, thoughts of defeat and failure are not part of the equation.
You remember what happens. The twelve spies go on their journey and return to make their report to the nation. Wih one voice, the twelve men speak of the richness of the land . . . it was indeed a land "flowing with milk and honey." But only two men, Calen and Joshua profess faith that God will give the Land to the people. Ten of the spies speak of defeat and failure. They despair: "The land that we have gone through as spies is a land that devours its inhabitants; and all the people that we saw in it are of great size . . . and to ourselves we seemed like grasshoppers, and so we seemed to them" (Num. 13.32-33).
These men had forgotten the assurance of God. Their failure disheartedned a nation that God would condemn to death in the wilderness.