"I... I know. He is my brother, and I want him to be my brother. I just... Everyone here knows Papyrus, not me. I... I'm not like him. And... I don't know if I'll ever be like him..."

He's supposed to protect his brothers, but he's already failed so many times at doing that. When he gets back to the lab, they'll surely destroy him so they can make a new shield...

Maybe that's where Papyrus came from, he notes with a pang of guilt.