Let it crash isn't about having the program crash, it's about the processes. It's a vocabulary issue for a lot of people, however. In erlang your program consists of multiple concurrent processes (well, that's the intention at least). When an individual process fails (say it's a parser and has been given bad input), the erlang way is to fail and let the supervisor/spawner figure out the corrective action. It's the same question we face when writing in java/c#/etc languages with exception handling. Where do I catch the exception?

A search example. You have several search algorithms given your input. Run all in parallel, if they crash it's fine. If all crash then the search was a bust, but if one succeeds you terminate the remainder and have your answer.