His downfall
When he allowed his humanity to cloud his survival instincts. He allowed himself to be lulled into a sense of security after he opened his home and heart for the women. It was foolish to not realize that either the mother/daughter would try to kill him- even if they had not did he think they would just go away, and not tell anyone of his existence. It was also foolish to think the men that raided his farm would not come back again. They should have left and moved away to safety and started new.
At least he found redemption for allowing the girl to escape.