It is from the "conversations" Peter Seewald was fortunate enough to share with Joseph Ratzinger, future Pope, and, I firmly believe, future Doctor of the Church. (Highly recommend the Ignatius Press book, by the way.)
Pain is part of being human. Anyone who really wanted to get rid of suffering would have to get rid of love before anything else, because there can be no love without suffering, because it always demands an element of self-sacrifice, because, given temperamental differences and the drama of situations, it will always bring with it renunciation and pain.
When we know that the way of love — this exodus, this going out of oneself — is the true way by which man becomes human, then we also understand that suffering is the process through which we mature. .... Anyone who has consistently avoided suffering does not understand other people; he becomes hard and selfish.
Love itself is a passion, something we endure. In love I experience first a happiness, a general feeling of happiness. ...
If we say that suffering is the inner side of love, we then also understand by it is so important to learn how to suffer — and why, conversely, the avoidance of suffering renders someone unfit to cope with life. He would be left with an existential emptiness, which could then only be combined with bitterness, with rejection, and no longer with any inner acceptance or progress toward maturity.