When I was in high school, we read the short story, "The Scarlett Ibis," by James Hurst. It's a very moving and inspirational story about family relations and the motivations that drive us sometimes to the point of cruelty. The relevant passage:

"There is within me, and with sadness I have noted it in others, a knot of cruelty, borne by the stream of love - much as our own blood sometimes bears the seeds of our destruction."

GeeDeeEmm