What even is distributed systems

Biased obviously, but personally I don’t think I “got” distributed systems conceptually until learning TLA⁺ or at least learning to think in the way it teaches you to think - in terms of invariants, liveness, fairness, and choosing grains of atomicity so you can model your system as a set of interacting state machines that generate infinite behavior traces. However, other people have certainly come to understand distributed systems without ever touching TLA⁺ so it is not the only path to that peak.