Of all the things I've seen in my time writing software I can qualify that some of the most fucked up things involved state machines. The worst of which was a 200 state hand written one in C for an embedded measurement system. There was no documentation, no comments and the states were numbered rather than named. The guy who wrote it originally was "anti RTOS" and had died after riding his motorbike recklessly leaving this shit for everyone to deal with.

It took me two weeks to do a trivial change because I had to reverse engineer a ton of it. And the only debugger I had was a couple of LEDs on the board I could wiggle on and off.