Defining any cultural group is difficult. This is not to say that a culture cannot be defined, but the definitions must be wide, loose, and flexible enough to incorporate variety, yet at the same time firm enough to describe the subject adequately. The task certainly seems daunting, but the solution is relatively simple.
Humans are social animals.
During infancy, the basic wiring for survival in society is established. Unfortunately, most people go through their lives unaware of this programming. They accept the reality that they are given. It is not until we leave our sphere and live among others that our programming becomes apparent. I am not referring to being a tourist, or living among our own in a foreign country.