(From my days a computer programmer...)

I was getting desperate to fix semi-rare "it just crashes" bug in one of my department's major programs. So I was writing a simple log of debug info to disk

I wrote it that so nothing was displayed, unless the crash happened ...

And I accidentally made the debug change 'live' ... {Blush!}

Then my coworkers started coming in, saying "What the heck is this?" So I explained.

A few days later, my coworkers started coming in again, saying "Hey. We like it. At least we know where the program is choking, and we know where to look. Leave it in."
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/geek alert/

The main program was an "assembler", reading the human readable code, line by line, and translating it to machine code. My debug file was recording each label in the program.

And I told my people they could put in dummy/unused labels to hone on the problem.
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Later I was able to fix the underlying bug, and issue an error message, instead of a crash plus debug file!