why we need friend?

Do you have friend?Why you need friends?Until now I haven't known why people need friends?

Many time,when we want to do something but we can't finish it we may need friend.This make me think of a word,a friend in need is a friend indeed.

I have seen a word in a book,if you feel lonely you may need a friend.But I don't think so.you feel lonely just because you can find a person to chat.