nfs as originally designed could not fail. so what happens when something that can not fail has a failure? that's right it hangs.

On the one hand this was kind of fun, network problems, the application hangs waiting on nfs, two days later you get everything sorted out and the application comes back never knew there was a problem.

On the other hand, this is the most infuriating behavior possible, everything you touch on the system starts freezing up. and you wish it would just fail so you could fix the infernal thing.

Later the "soft" option was added so that nfs could actually fail.

It's true that error management is critical for a production environment, but from a pedagogic point of view, they can left as an "exercise for the reader".