I was recommended a book by a friend many years ago. It was called "The First Deadly Sin" and puts the reader in the mind of a serial killer. It was horrifying to me, exceptionally well written, but if affected me for a long time. I hated being in that character's mind... I'm not a weak person, but it disturbed me so much to think this was how some people actually thought. Ugh. Should have thrown it away like you did, but I had this dumb pride in always finishing books I started. That changed with "The Shining". After the character went after his kid, that was it for me.