If you ask one hundred people to do a task (particularly one that involves following instructions or using a computer or both), figure that two of them will mess it up.

It doesn't matter if you use ALL CAPITAL LETTERS. It doesn't matter if your instructions are crystal clear. It doesn't matter if you ask them to sign a release. Two percent will mess it up. And it won't always be the same two percent either, so the idea of kicking the clueless out won't work.

Which means you only have two choices:

• Design systems that have the good sense and gracefulness to permit the 2% to proceed, or
• Annoy, demonize or lose these people

Technologists hate this choice, but it's true. We have to plan for human failure and part of our job is to have the resources and back up to allow these people to remain in our tribe even though they're unable to follow a simple instruction.

[Can I just clarify that the first choice isn't the only choice. Plenty of successful designers (including Apple) gladly choose the second. Pleasing everyone isn't required. Making the choice intentionally is.]