Because we are human. But a human is a species with herd habit. We need the people around us, as the pieces of society, to coexist and thrive. Friends help each other in difficult times, share joys, relieve sadness. Without friends, we just existed. Exist in an isolated and narrow world.
And in that small world, there will be times when we fall down, sad, lonely, need a lot of help to help us get up. Otherwise we will destroy ourselves. Then, is the time when we most need friendship. Is at that we are miss you most. But there should be a couple of times like that, right. Because those times allow us to understand and cherish the friendship better. Not only lonely sad times, but also happy and happy times, we always remember to be happy with friends.