2% of your customers don't get it. They won't read the instructions, they'll use the wrong handle, they'll ignore the warning about using IE6. They will blame you for giving them a virus or will change the recipe even though you ask them not to.
And not only that, they'll blame you when things go wrong.
If you do a very, very good job of design and UX and process analysis, you can lower this number to 1%.
But then what?
The thing is, blaming this group for getting it wrong helps no one. They don't want to be blamed, and they're not going to learn.
The other challenge, of course, is that the 1% keep changing. If they were always the same people, you could happily fire them. But there's no way to know in advance who's going to get it wrong.
If you're going to be in a mass market business, you have no choice to but to accept that this group exists. And to embrace them. Not to blame them, but to love them. Successful businesses have the resilience to make it easy for them to recover. To make it easy for these people to find you and to blame you and to get the help they need.
Sure, whittle down the number. But the ones who are left? They're part of the deal.