Years ago as an intern at Microsoft, I had code go into the Excel, PowerPoint, Word, Outlook, and shared Office code. Excel is an incomprehensible maze of #defines and macros, PowerPoint is a Golden Temple of overly-object-oriented insanity, and Word is just so old and brittle you'd expect it to turn to dust by committing. There are "don't touch this!"-like messages left near the main loop _since roughly 1990_. I had…
Frequently there are critical code sections where it is much easier to tell people "don't touch it" rather than training people how to work on it safely.