This is one of those posts that I’m mostly writing so that I can repetitively link to it whenever I use this construct, so I don’t have to keep explaining myself over and over. As such, it is one of the few posts that I’ll likely edit, so if you see changes, I’m just trying to make sure I’m accurate and complete.
Please note that this is all just a summation of research done by a number of smart people over a great deal of time. I’ve tried to explain it as clearly as possible, but the real credit is with the social psychologist, economists, and others that have worked on it (and who are too numerous to name).
Opposing forces (or dual process) theory is my psych shorthand for a powerful but relatively simple way of understanding human behavior. Speaking in sweeping generalizations, all decisions and behaviors are the the product of two fundamentally opposing sets of forces: reasons to do something (promoting pressures) and reasons not to do something (inhibiting pressures). These can be internally or externally generated, and how receptive you are to internal vs external cues can itself be acted upon.
The reason this is such an important concept in behavioral change is that if you want to inspire a particular behavior that is not already occurring (or make an existing behavior occur more or less frequently), you start by understanding the balance of forces behind the current state of the world. Once you know why people are doing what they are doing, you can figure out whether you need to remove obstacles or place more in the way, or make something more or less rewarding.
Generally speaking, I see companies (and non-profits and the government) leap towards promoting explanations much too quickly. Want people to eat healthy? Most programs are about telling people why it is important (promoting pressure). But the answer most likely to yield results? Make healthy food cheaper and easier to get (inhibiting pressures). Most people love strawberries (they already have plenty of promoting pressure) but not when they cost three times as much as a bag of pretzels and are in terrible shape at your corner bodega.