Check your inputs -- Save your job!
At various times in my 10 years of Identity Management Consulting and 25 years working in the IT industry I have been asked to clean up various messes generated by those before me. Some of those messes involved disk failure or other issues that couldn’t be completely prevented. But some involved automated process that didn’t check their inputs. If garbage into a computer gives you garbage out, then garbage into an automated process that doesn’t check its inputs gives you a meltdown!