[ToValueFunfetti]

To elaborate on this, if I swear on my mother's grave, I'm pinning my respect for the oath to my respect for my dead mother. If I violate the oath, I'm also violating something I consider sacred. My mother never has to find out for me to feel the consequences.

Probably this doesn't work on everybody. Even if it only works on 5%, it's essentially free so why not?

[klodolph]

Yes, and I think if we follow that scenario further, we can imagine ways it would play out. “Alice swore an oath on her mother’s grave, and then violated that oath? Wow, Alice really can’t be trusted.”

The oath is a symbolic ritual that communicates something to other people around you.