What they found was that it wasn’t the overall amount of money won in the game that gave the participants the greatest happiness. The formula incorporates a “forgetting factor”—which predicts that the happiness obtained from a previous win degrades over time. Ten more trials after a win, the original win “essentially has no influence on current happiness.”

According to the formula, happiness spikes when things go better than expected. “For example,” the study concludes, “a £0 prize decreases happiness if the alternative was winning £2, but increases happiness if the alternative was losing £2.”

Which makes perfect sense: It’s better to win when that win avoids a bigger loss. But what’s surprising about this study is that the researchers were then able to use that formula to predict the general pattern of happiness in more than 18,000 people playing a similar game on a smartphone.