As humans are fallible, it's inevitable we will make mistakes carrying out even what we intend to do, when we know it and are actively trying to do the right thing.

Sometimes our mistakes are not recognizing the right thing to be done, or not recognizing anything at all.

I think the view that true security is impossible is true if security is up to one person. What about a system with multiple layers of sign-off, or an automated system that can help test the security of what you're doing and alert/prevent dangerous behaviour without specific reasons.