I have confidence in certain people that they will follow a given protocol to the best of their ability. They're not vouching for someone: they're indicating t

I have confidence in certain people that they will follow a given protocol to the best of their ability. They're not vouching for someone: they're indicating the successful completion of a keysigning protocol. But again: you don't have to trust a single person. As more people sign Alice's key, it's increasingly unlikely that Alice fooled every one of those people.