Corollary: pick a starting point, and add a shit-ton of logging to trace what is actually going on. Hide it under #if DEBUG if necessary, and hope that you don't get a Schrodinger's Code situation where observing the code changes how it behaves.

I've had a few more-or-less realtime multithreaded projects that I've worked on where you can't really put a debugger on a system and halt it, without breaking things in interesting and misleading ways, and the only good option is to fall back to ye olde printf debugging.