Lewis argues that this drive will exist in me to some extent forever. The feeling of being "left out" is horrible, and so this causes people to commit to things that they aren't really interested in or don't bring glory to God's name. They sign onto these activities solely because they want to avoid the feeling of curiosity and jealousy.
It's important to have friends, and even to belong to groups as long as they support the gifts that God has given you and they compliment your interests. It makes no sense to sign onto something you don't agree with, yet we do it so often. We want to discover these "insides" but are warned that we will not receive anything true and good if we pursue them.