Wow, here in the USA, I never have issues like this. Where I'm at, all the people with huge carts filled with food go to the checkout lines. The only people who use the self-checkout are people with 1-15 items. There usually are at least 6 self-checkout terminals. I look at the checkout counter with a live employee and the are without doubt, always always always so much slower, because they will have 3 people in line with 50+ items.

I think if someone brought 50 items to self-checkout area, they would get knifed in the back.

There are usually at least 6 terminals, so if you have a incompetent idiot on one of them, it doesn't make too much of a difference.

About 90% of the time, there's no line.