PoW systems rely on the "phone a friend method" as well. When you download a Bitcoin client from a "friend", you are trusting them to honestly introduce you to the network. If you fall asleep for a period of years, you have to trust your friends to honestly inform you of all of the PoW forks and policy changes that have occurred over that interval. The only difference is that PoS blockchain clients must be bundled with a modestly-recent block hash along with the thousands of lines of code that you have no practical way to audit.
The problem eventually reduces to Ken Thompson's "Trusting Trust" [1] problem. There's no way to externally validate the honesty of any system (cryptocurrency, or otherwise).
The problem eventually reduces to Ken Thompson's "Trusting Trust" [1] problem. There's no way to externally validate the honesty of any system (cryptocurrency, or otherwise).
[1] https://www.cs.cmu.edu/~rdriley/487/papers/Thompson_1984_Ref...