If you don't learn something from pushing a debug build to production, your debug build isn't instrumented enough. Maybe all you learn is what the effect of building with/without optimisation is on the real workload.

There's practically an entire genre of "here's what I learned from my expensive mistake" stories. Usually they teach humility and caution. This one is interesting because it's a variant of YAGNI. Imagine that you've carefully tuned your (software/car) for a specific set of parameters, then throw one out of whack by mistake - does this get caught by monitoring? Do you even notice? If you hillclimb from the new status to an optimal one, do you get back to the same local optimum?

Then of course there's the famous RISKS digest, which can be funny or depressing depending on your mood and dependence on complex systems.

(My own personal one of these? "killall" behaves differently on Solaris than it does on Linux ..)