A usable design lets someone complete the task without becoming a demonstration of their difficulty.

Finishing the task is only part of what a good design provides. The other part is doing it without an audience, without calling someone over, without a queue forming while you explain what you need. A machine that only works with help turns a private errand into a public event. Independence and dignity are the same thing in practice.

Look at something you have built or chosen and ask whether a person could finish with it alone and unobserved. Fix the step that requires asking. That change usually costs less than it appears to and is felt every single time.