[lemonforest]

It's just a mental construct such that if you know frank is really real and frank knows jenny is really real, it's fair to assume that jenny, who is frank has vouched for, is who she claims to be. But you aren't forced to trust that jenny is really jenny either.

Wiki usually does a better job of explaining stuff but I can always use the practice... https://en.wikipedia.org/wiki/Web_of_trust