The pleasure trap is about evolutionary mismatch. When an organism is presented with a super-normal stimuli that did not exist during our ancestral history, it can trick our evolved psychological mechanisms that are designed to optimize our health and happiness. This is because all animals are designed by evolution to feel good about doing things that are adaptive (promote survival and reproduction), and when an organism is biologically successful it gets a "dopamine hit" which activates the pleasure centers of the brain and that behavior is reinforced. The organism is rewarded for engaging in behavior that improves the probability of genetic success. A super-normal stimuli is something that doesn't exist in nature but lights up this neurology all the same (drugs, porn, processed food, video games, television, etc.) The result is people will overindulge in these easy pleasures at a cost to their health and long term happiness.
This is a particularly tricky problem to deal with, because one has to fight one's own instincts. For example, all organisms have pre-wired circuits that say "you should eat the most high calorie food in the environment", this is because we evolved surrounded by food scarcity. With today's abundance of rich food (the western diet), it takes large amounts of self-control, planning, diligence and awareness to avoid this pleasure trap. That is why most people in western culture are in the pleasure trap in relation to their diet and don't even realize it. As a result deficiency diseases are basically gone but there has been a skyrocket in diseases associated with excess (high blood pressure, diabetes, strokes, gout, etc.), yet people feel powerless in the face of this drug like food.
The problem is much deeper than simply a dietary crisis, and we have Dr. Lisle and Goldhamer for discovering, describing and prescribing a solution to it in their book The Pleasure Trap. It is one of the best examples of how evolutionary thinking can have some profound application to improve lives and help people optimize their health and happiness.
Further Reading
The Pleasure Trap: mastering the hidden forces that undermine health and happiness
By Douglas Lisle, Ph. D and Allan Goldhamer D.C.