I think that the purpose of S.E. Hinton's the Outsiders was to show people that life is hard and that even when things are looking down usually you just have to work through it.
I think this because a lot of times in the book it seemed as if there was no hope but they continued through and worked hard and everything got at least a little better. Like when ponyboy got jumped and then his brothers helped him. At first it seemed that ponyboy would die but it got better.