One issue is that failures are not necessarily contained. An error in a less important area could still corrupt the state of something more important. The most

One issue is that failures are not necessarily contained. An error in a less important area could still corrupt the state of something more important. The most convincing take on this I've seen is Erlang/Elixir. You generally fail fast there, but each program is composed of many different, isolated processes. No matter how a single process fails, it won't affect any other independent processes. A stopped process only takes down those processes that depend on it, everything else continues. And Supervisors can restart the failed processes from a known good state again.