I'm currently in a consulting gig coming up on my one-year anniversary. I'm helping maintain an internal development tool that was written by the company's CTO over the course of the last 30 years. It's some of the most godawful code I have ever seen: functions that are many hundreds of lines long, lines that are many hundreds of characters wide, weird state dependencies all over the place. It is literally impossible to work on this code base on a laptop. My client has two enormous 5k monitors on his desk. (I have to muddle through with just one 4k monitor, and that's barely adequate.)

And yet... somehow, it all works, and at the end of the day, they ship their product on time and make a boatload of money. So my visceral reaction to this code is a very strange mixture of horror and respect.

My approach to trying to get this mess fixed is something along the lines of, "You're the boss, and it's your call, but if I were one of your investors I would be very concerned about the long-term maintainability of this system if, God forbid, something were to happen to you."

Does this approach work? Hard to say. No substantive changes have been made. But I haven't gotten fired either.