I think we need to give grocery shoppers a break. We are all guilty of parking our cart and then standing in front of the shelves to look for something. And when you are thinking of your list it is easy to get distracted.
A long time ago waaaay back when my kids were small there was a magazine article about how grocery shopping can be one of the most stressful things a person does. And this was when I got to go grocery shopping on Saturday night because I could go by myself without children or husband! Big Saturday night date night!