People are stupid.
Everyone, including myself of course, is stupid in one way or another. Let's take my summer job for example. I worked for Meijer, which is a chain of superstores in the midwest. I told them as they started unloading their groceries that this is an express lane and that they'll have to go to a normal lane. Another time I was working a normal lane, without a bagger, so I had my second belt down, my terminal turned, and I was standing in the direct line of the belt so I could go quicker.