We see everything through the eyes of the mother, and she is an unreliable narrator. She admits she never wanted Kevin. She broke his arm, and who has a seven year old still in diapers without taking them to all kinds of doctors to find out why? She assumes he’s just being a pain in the ass. And she was insufferably elitist and superior. So I do wonder how much was Kevin and how much was mother. Which is exactly what we’re supposed to wonder.