Have you never been at work being forced to do something because you need money but you just are not feeling it that day? Obvious mistakes will ALWAYS happen, regardless of rules, regulations, human involvement, process, etc. It's thoughts like this

"How can we make sure this doesn't happen again"

"Its unacceptable than an obvious mistake happened"

that make corporations so full of random rules, because they think it's possible to prevent things like this. What matters is the frequency with which they happen, and how gracefully you handle yourself after it happened.