I think it is very easy for the average person to forget or not realize how incredibly easy it is to get calories into the body and how little food is necessary to do so. Most people in the world (I know, this is not everywhere and everyone), live in an era of food abundance. It's cheap enough, extremely accessible, often easy to eat or ready to eat, and that has simply made it very convenient to get calories in, often while barely thinking about it. Mindless eating, not thinking about what you should eat, etc. All of these factors have played into why obesity is such a problem (at least in the USA).