Our human being are social animals. Therefore, we can not just live alone.
I like to observe people wherever I go. As an international student, it's natural for me to look for similarity and difference among people here to compare with my home country. One thing common everywhere I realized is that people instinctively like to be with the people who is similar to them when they are new to some situation. Think about you are totally new to a country, are you willing to stay with your countryman or local people?
I guess countryman is the answer in majority. Here is what I see. Foreign people from all over the world in Shanghai tend to form different circles of their countries although many of them keep a good balance. At the same time, this, to some extent, explains the association naturally formed by different countries' people in US, one of a famous example is China Town.
It's understandable. People are nervous, anxious and stressed when they are in a strange place alone without any support. Consequently, being a member of some groups deindividualize them and bring them a sense of safety and comfort. The concept of conformity also somewhat explains it. Most of the people doing conforming in order to comfort themselves. Without doubt, the feeling of comfort is nice.
For my own, I prefer with the people who is not that similar to me, no matter where they come from and what their personalities are. I believe diversity makes the world more enjoyable. Difference doesn't always bring anxiety. It also means unique and brings surprise. Similarity doesn't necessary mean comfort. It also tends to be limited and stays monotonous.
Most of the concepts in psychology up to now are impressive to me, especially for social psychology and personality part, because they reveal the true face of individual difference and individual similarity.