How many times have you heard there's been a big accident, whether it's a plane accident, a train accident or something like that, and people say, "Oh, it was human error."? Right? It was due to human error. The person didn't do the right thing at the right point; they didn't notice something that was important, and things went wrong. So, just imagine instead the wing falls off the plane because there's metal fatigue where the wing joined the plane. Now, you would say it was due to the metal fatigue, but you wouldn't say, "It was metal error."
You would say it's a *design error* because the designer of the plane, the engineers, the detail designers *should have* understood the nature of metal and the fact that you do get metal fatigue after a while. You should either design it so that where there's metal fatigue it *doesn't fundamentally mean the plane will crash*, or you design it so that you can *detect* when that metal fatigue is happening and then *take preventive maintenance*. There are a number of strategies you've got because you *understand*
metal as a material *has known ways of failing*. We as humans have *limits and constraints* and *ways that we fail* in the sense we don't always do things in the perfect way – just like a piece of metal doesn't. As a designer, your job is to *understand those limitations* of people as actors in the system and *ensure the design of the system as a whole works even when those happen*.
So, whenever you hear about human error, it was human error! But typically it wasn't the operator or the pilot or the nurse or the doctor in the hospital; it was typically the *designer of the system* that's there. If you treat users *as well* as a piece of metal, you probably are dealing with them a lot better than they usually are dealt with. The user is at the *heart* of what you do. But *understand* those users – understand the nature of them.
And so, *then* you'll start to treat them far better, hopefully, than a piece of metal.