Why does winning five dollars sometimes make you happier than winning fifty? According to a team of neuroscientists, the secret lies not in the amount itself, but in what you expected to happen.

In a study published in the Proceedings of the National Academy of Sciences, researchers led by Robb Rutledge of University College London unveiled a new model of momentary happiness. Their findings suggest that our moods rise and fall less with absolute rewards and more with how reality stacks up against our expectations.

The experiments were deceptively simple. Volunteers played a decision-making game in which they chose between guaranteed payoffs and risky gambles, then rated their happiness. Some participants completed the task inside brain scanners, while more than 18,000 others joined in via a smartphone app.

It’s all about expectations

The results were striking. People’s happiness increased not just when they won money, but especially when the outcome was better than expected. Conversely, when events fell short of expectations, moods dipped—even if the player still earned a reward.

“Expectations play a central role,” the researchers wrote. “Happiness is strongly influenced by recent outcomes relative to those expectations.” Brain scans backed this up, showing activity in the ventral striatum, a region tied to reward processing, tracking these shifts in mood.

Real-world and lab data

The study’s scale added weight to its conclusions. By combining traditional lab work with large-scale app-based data, the team demonstrated that the same psychological and neural mechanisms govern fleeting feelings of happiness both in controlled settings and in daily life.

The findings may seem intuitive—who doesn’t enjoy a pleasant surprise?—but the research goes further, offering a quantitative model that predicts how expectations and outcomes interact to shape moment-to-moment well-being. Scientists say such insights could eventually help explain mood disorders and guide new treatments.

For the rest of us, the takeaway is clear: managing our expectations may be just as important as chasing rewards. After all, happiness, it seems, is not simply about what we get, but whether life delivers more—or less—than we bargained for.