You can’t run the microwave with the door open. There’s a cut-off switch that won’t let it turn on until the door is closed.
On the other hand, there’s nothing at all keeping you from putting a big bowl of silverware and a can of spray paint in the microwave and blowing up your house.
Your car might not let you switch to Drive unless you press the brake first. That’s because people who weren’t paying attention were slamming their Audis into the walls of their garage, thinking that they were hitting the brake, not the gas. So Audi installed a poka-yoke. It was easier than teaching people how to use the pedals the way they intended.
Sending a manuscript to a freelance copyeditor before you submit it to your publisher is a self-built poka-yoke. As is handing over the keys to your partner when you get to a cocktail party.
You can add a poka-yoke to just about any system that is fraught, or one where you’re nervous about the outcome.