Every Erlang process in the universe should be addressable, and trace backed if we wish they will talk together. - Joe Armstrong

When I'm writing a program, my approach is to "write a bit" and then "test a bit." I start with a small module with few functions, and then I compile it and test it with a few commands in the shell. Once I'm happy with it, I write a few more functions, compile them, test them, and so on. (page 60)

The cornerstones of fault tolerant programming are to isolate errors to make sure if one thing crash it does not crash anything else. That's what the processes in operating system do.

So what's wrong with the shell? and what's wrong with Erlang? It's not LISP!