The 20-second rule is the principle that if you make something 20-second easier to do, you are more likely to do it. By contrast, if you make something 20-second harder to do, you are less likely to do it.
Thus, seemingly trivial adjustment can have a huge impact on our habit forming. For instance, resisting temptations like junk food becomes more challenging when they’re easily visible and within close reach. Therefore, we need to make them harder to access.