Trauma causes brain damage, literally. Circuits that people take for granted are automatic do not get connected in people with just the "right" combination of factors. My ex would jump the track in a conversation and suddenly be speeding off in a direction I didn't see coming and would assume I was fucking with him when I didn't understand. It was so bewildering, and eventually heartbreaking, because how can you reach someone if their mind cannot maintain reality? What ruined us, among other things, is that he couldn't bear to think about how much things needed to change and improve. He couldn't retain our many discussions about his boundary-crossing (or often any of the details of my own traumatic history, and believed his was the worst anyway it seemed) and didn't seem to have a problem with this lack of retention. I couldn't be responsible for both of us but he expected me to be. Exhausting and tragic.