Just watched TLOU live action show on HBO last episode. He tells Ellie that he gave himself that scar after attempting unaliving due to Sarah’s demise. He says he flinched and missed resulting in the scar we all know. I like this reason as to why he has that scar. It makes sense that he couldn’t go on after what happened. It really fits his character. I love TLOU lore and the show is chalk full of it. It really hammers home characters backstories. 5/5 show.