Social rejection is what leads to Hauchecorne becoming unhinged and obsessed with the act of bending to pick up a piece of string.

Hauchecorne used to pride himself on being a tricky man. He paraded that trickery and used it in his business dealings. It was something that people took as true about Hauchecorne. This is why, when he insists he didn't steal the purse, the people in the town don't believe him. They assume his actions based on what they know of him, and they believe that he is a person who would steal.

This leads to a great deal of social rejection from the community. While he may have suffered from a bruise if he'd been assaulted in the wake of stealing, that would have faded over the weeks. The social rejection continues to pain him because it is a pain that can't entirely heal as long as a person is still being rejected.

Hauchecorne becomes obsessed with explaining what happened; he wants people to believe him. No matter what he says, though, they refuse to. His pain isn't visible like a cut or a bruise, but it influences him more keenly and for longer than either of those would. Even on his deathbed, he's still trying to explain his innocence and gain back the social respect of the town.