Have you ever found yourself daydreaming about a day, perhaps not too far in the future, where you’ve finally gotten something you really want and just feel happy? Of course you have; this is a very common thing for people to do. They are sure that if they just lose the weight, get the job, or start dating the dreamboat that it will be happily ever after.

Predicting how your future self will react emotionally to an event is called affective forecasting. In general, people’s forecasts of future emotions don’t match well with their actual reactions when the event happens. They tend to think they’ll react more strongly and that the feelings will last longer than they actually do. People also forget that they won’t experience the event in a vacuum; their emotions will also be affected by all of the other things going on in their lives.

Let’s say someone wins the lottery. They’ve always said would solve all their problems; no more worrying about bills, being able to take a nice vacation, and finally being able to walk away from an unsatisfying job. At first, things really do feel great. But as time passes, their happiness begins to fade. Little by little, the person’s excitement simmers lower until eventually, their mood is back to about where it started. Being a lottery winner becomes the new normal, not a source of daily pleasure.

This return to a baseline happiness level is known as the hedonic treadmill. On a treadmill, no matter how hard people run, they remain in the same spot. Similarly, in the pursuit of happiness, people may achieve amazing things, but after some time, they end up roughlyjust as happy as they were when they started.

Does this mean that behavior change can’t make people happy? Not exactly. Behavior change is not likely to leave people in a state of lifelong ecstasy, no matter how badly they wanted the result. But it can help people feel more content by removing specific stressors from their lives. And, depending on what behaviors have changed, they may bring new, happiness-enhancing possibilities with them. Imagine the ex-smoker who can now breathe deeply enough to think about hiking in the mountains, or the savvy saver who can afford to think about a planned retirement.

When people expect behavior change to make them happy and it doesn’t, they may go on to downplay the importance of small changes in their overall well-being. They incorrectly assume that more is better, and seek bigger targets. Instead of focusing on realistic yet meaningful steps toward a goal, they pursue bigger changes instead.

Bigger changes, of course, are harder to achieve. And so people are more likely to fail. They may experience a rollercoaster of negative emotions as they fall short of their big goal. And there’s the opportunity cost of working on something grandiose at the expense of smaller tasks that add up to meaningful change. Worst of all, science tells us that those people who do reach their impressive goals won’t stay happy for long.

The people who manage the hedonic treadmill best are the ones who treat it either like a series of sprints (chasing smaller goals more quickly) or a marathon (chasing bigger goals at a steady pace). Trying to do both by sprinting a marathon usually ends badly.