请帮忙解释如下英文句子意思解释最后一句,表面意思都能看懂,只是不理解这句话想表达什么意思?是否与国外的某些习惯有关?如下

请帮忙解释如下英文句子意思
解释最后一句,表面意思都能看懂,只是不理解这句话想表达什么意思?是否与国外的某些习惯有关?如下是上下文,供参考
Since I started working part time at a grocery store,I have learned that a customer is more than someone who buys something.To me,a customer is a person whose memory fails entirely once he or she starts to push a shopping cart.One of the first things customers forget is how to count.There is no other way to explain how so many people get in their express line,which is clearly marked 15 items or less,with 20,25 or even a cart load of items.