Individualism
Americans usually view every person as self-sufficient individual, and this idea is important to understanding the American value system. Everyone is their own person, not a representative of a family, community, or any other group.
You may view this as rather selfish and egotistical, or as a welcomed freedom from the restraints of family, community, social class, etc. Yet, this self-centered attitude prevails in American culture—placing the most importance on the individual, not the group.
Likewise, U.S. Americans do not like to think of themselves as being dependent upon others or as others being dependent upon them. This can affect the boundaries placed on personal relationships, which starts with friendships.