The majority of self-checkouts I've tried were such a clusterfuck of bad UI design, and it's made worse by the requirement to have a human check your ID when you're buying alcohol etc., which is a huge bottleneck when a lot of people are using SC. And when you inevitably push some wrong button that puts you into a situation you can't get out of without employee intervention, you (as an introvert) are in a far worse situation than if you had just used a regular checkout (though cashiers in my country don't really do small-talk, which obviously helps a lot from an introvert perspective).