Toothpaste had a similar trajectory.Manufacturers enjoyed great success when they added flavors like spearmint, peppermint, and cinnamon to their products.These flavors don’t improve the effectiveness of toothpaste.They simply create a “clean mouth” feel and make the experience of brushing your teeth more pleasurable.My wife actually stopped using Sensodyne because she didn’t like the aftertaste.She switched to a brand with a stronger mint flavor, which proved to be more satisfying.Conversely, if an experience is not satisfying, we have little reason to repeat it.In my research, I came across the story of a woman who had a narcissistic relative who drove her nuts.In an attempt to spend less time with this egomaniac, she acted as dull and as boring as possible whenever he was around.Within a few encounters, he started avoiding her because he found her so uninteresting.Stories like these are evidence of the Cardinal Rule of Behavior Change: What is rewarded is repeated.What is punished is avoided.You learn what to do in the future based on what you were rewarded for doing (or punished for doing) in the past.Positive emotions cultivate habits.Negative emotions destroy them.