"When I went mental, after Nev told me that Ron was regularly hurting you, I ...I totally lost control," Harry mumbled. "I lost my mind wholly. I only remember what happened because Narcissa reconnected my recollections of it. I'd actually sliced the memory away from my own conscious mind. But I had to know ... know what my worst looked like, so that I might learn how to control it. Or, at least, recognise the signs, so I could take myself away from anyone I might hurt.