Why do people come to the 20 items or less line with 40-50 items?

I normally work as a stocker, but I have been called up to work the register all this weekend because of increased customer traffic. I was at the Speedy Checkout this weekend and I have had at least 2 people come through with items over the limit! One customer had 41 items, according to the receipt print-out. Before the transaction, he asked if I was "counting items," as if he KNEW he was not supposed to be in this line. I said I was not counting, so I went on and checked him out, because there's really not much you can say without them going ballistic on you. Next day (Easter), this woman saw me looking at her buggy and said with an attitude "Don't look at me because I'm not going anywhere else!" She had at least 55 items in her buggy, and while i was scanning them, some of the customers behind her we quite upset. They had only 3 or 4 items, while she had 55. Most of those other customers were dressed up and in a hurry (possibly Easter Serivce or dinner). Why are some people selfish?