turtles all the way down
expressionprogrammingcryptography
The recursion joke applied to trust: every layer rests on another layer, and eventually you must simply stand somewhere.
PKI ends at self-signed root CAs, DNS at the root servers, secure boot at a burned-in key - every chain of trust bottoms out in an anchor taken on faith. Naming the turtles is how you find out what you are actually trusting.