when you win you share the success, and when you lose, you have someone to share the loose with.

a player might feel that he/ she is a disappointment to his team if it doesn't do well, even though this person is quite a good player.

playing in a team can also help one make new friends and feel the sense of belonging.

There is a chance that not all players will get on with each other. This may cause arguments and make players very competitive.

the sense of team spirit and team pride one feels.

players learn to cooperate while working towards the same goal. This encourage people to be less selfish.