I personally believe that greed is the source of all suffering. We have desire to acquire, and when we fail to reach that objective, we suffer. Though the sense of belonging in the human-nature is extremely strong, attachment to something or someone could also bring suffering. When things do not go the way we wish, or someone you loves doesn’t love you back, that always bring about great suffering.
Although there are no definite solution to approach the problem of suffering, the idea of karma could be the key to helping us deal with how we view suffering. If karma is a cosmic laws that says we get serve what we deserve, we all will try to approach things differently: better. For me, I will do good things and hope that it will come back to me eventually. Though it doesn’t come up in an obvious way, at least it gives me something to look forward to.