Let just pretend this person joined two groups. He joined the group where this group liked soccer. But he does not like anything about soccer and there is a distance between him and the group. Therefore, he may leave the group.
Later, he joined another group of people who liked to play computer games. He himself more of the person who loved to played games like counterstrike and the people there also liked playing there. So he enjoyed himself there very much.
Oh man, Sherman Lum, what are you talking about? One group loved to play computer games and one group loved to play soccer. What am I relating to? Interests!!! Normally group has one or more common interests and some introverts may be left out because they may not like the interests the group held.
Source:
http://www.cartoonstock.com/lowres/rje0382l.jpg