The supermarket bill shock

Which of the two is more predictable – your supermarket bill or your restaurant bill?

Most restaurant orders comprise of a starter, a main course and a dessert or a drink. Our mind is good at estimating the overall price of two or three items quite well. When I receive bills at restaurants, it is usually within the bounds of how much I expect.

On the other hand, I have done the most routine shopping at a supermarket and stared in disbelief at my bill after I’m done.

“€40! That can’t really be correct!”

I have been so surprised on occasions that I have stopped to cross-check the computer generated invoice for arithmetic mistakes. Of course, when I do add up the prices of two avocados, that large jar of Nutella, the packet of organic mozzarella cheese, almond milk and the ten other little things on my list, I find no math errors – just errors in my own perception.

But why does this difference exist? Why are restaurant bills digestible, while supermarket bills aren’t?

The answer has much to do with how many things we can hold at any given time in our head. Our working memory is limited to holding about 4 things at any given time. In case we provide it with more than four things, it lets go of some information to accommodate the additions. In effect, we easily remember the four things we ordered at a restaurant, but our mind cannot account for every single item as they continue to stack up into our shopping cart.

This design of how our minds work is key to the business of running supermarket, and also why we end up over shopping on most of our visits there! We could also use the same principle, though, to our advantage – by breaking up larger projects or assignments into smaller chunks, while breaking up our workdays into a to-do list of smaller activities. That way, our working memory is often freed up to focus on whatever is the most essential task at hand in any given moment.

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