We were like grasshoppers in our eyes, and so we were in their eyes (13:33)
The Yalkut Shimoni (quoting Midrash Tanchuma) explains: Hashem said to the spies, “You said, ‘we were like grasshoppers in our eyes.’ For that, I forgive you. But why did you say, ‘and so we were in their eyes’? Who told you that you were not like angels? How do you know what I caused them to think?”
It was this tragic mistake that brought the 40-year punishment. When a person has a distorted and deflated perception of himself, he may totally lose his proper perspective.
While others may view him as an angel, he thinks they see him as a grasshopper. When we see ourselves as insignificant, we have no doubts that others see us the same way, and we are right. People do tend to perceive us as we perceive ourselves. [The Chofetz Chaim] (The Torah Treasury)