However think of all the things that can go wrong with your environment that don't involve a bug in your program. A network connection goes down, the disk gets full, &c. All of those can be handled without unwinding the stack to the point where the code for handling them was defined.

For a really trivial example, consider a performance watchdog. If you want to completely abort the attempt and log a call-stack, you can do that it just about any modern, dynamic language because the exception object includes the call-stack. But what if you want to log the call-stack and continue for the first N times the watchdog rolls-over? This is, of course, doable in other languages with passing callbacks and such, but in Lisp this can be done by signalling a condition in the exact same manner that an exceptional condition would be signaled.

I'm excited about this book, because that particular feature is underutilized in Lisp (by myself included), probably because it's one of the last dynamic things that Lisp does that more well-known dynamic languages do not, so programmers coming from other languages just aren't going to use it.

Nitpick: the only thing that cannot be handled by winding the stack is when you run out of stack to wind.

But, luckily, if your program overflows the stack, you usually have bigger issues to deal with and/or you usually have all the stack information you need to diagnose the problem.