Secure or random reward? The effect of motivating uncertainty

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In a travelling amusement park there is a stall, run by an elderly gentleman, who invites visitors to the park to challenge him in his game, in exchange of a prize. The objective is simple: to score a certain number of baskets within a set time limit, with only one attempt available.

The challenge is not particularly difficult, nor is it too easy, so you have to try, but there is one condition. Before playing, the elderly gentleman chooses whether to give a safe prize, 2 euros for example, or a randomly chosen reward, 1 euro or 2 euros, and communicates this to the visitors. The visitors choose to play anyway, as the old man is kind enough not to charge any tickets.

The strange fact is that, disregarding the ability of the participants, the visitors destined to receive the random reward seem to be more engaged and motivated. Why does this happen? It seems that the random component influences people’s engagement, leading them to perform more. This bias is called the motivating uncertainty effect and has been studied in depth by researchers.

Four experiments and three hypotheses

In a 2015 study, researchers conducted four different experiments to understand the mechanisms behind this bias and test their three hypotheses. They first postulated that an uncertain reward, even if of lesser value, was more motivating than a fixed reward. In the second hypothesis, they assumed that this effect was present when the subject focused on the process rather than the outcome. Finally, they hypothesised that uncertainty would generate a positive experience, which in turn would increase motivation.

The researchers defined motivation as the amount of time, effort and money invested to achieve the goal; they based their hypothesis on the fact that people are innately optimistic, which previous studies seemed to show. Having found enough volunteers, they started the study: we will look at the first and the third one, mentioning the results of the other experiments as well.

In a travelling amusement park there is a stall, run by an elderly gentleman, who invites visitors to the park to challenge him...

Being paid to drink water

In the first experiment, the researchers divided the subjects into two groups, one with a fixed reward, $2, and the other with an uncertain reward, $1 or $2. The challenge was to drink at least 1.4 litres of water from a 3.8-litre jug in two minutes.

The experiment was conducted individually, and 87 students participated. The results were surprising. While in the group with the fixed reward only 43% of the participants completed the challenge, in the other group 70% drank at least 1.4 litres of water! An increase of 27%. Uncertainty increased motivation, more so than a smaller reward could decrease it.

In this experiment, the probability of a fixed or uncertain reward was 50%. In the second experiment, the method and probability changed, but the results were similar.

Chocolate at auction

In the third experiment, the effect of focusing on the process or the final result was examined more closely using a popular motivator: chocolate. This experiment consisted of participating in an auction for a bag of chocolates. The effect of uncertainty as a motivator was tested by dividing the groups by the number of chocolates, either certain or random, and the hypothesis that focusing on the process, rather than on the result, would generate more motivation, was tested by creating both auctions with bids and auctions with sealed envelopes.

In the bidding auctions, the uncertain prize attracted higher bids, influenced by the fact that, with eight bidding rounds to go through, volunteers were more focused on the process than the reward. In contrast, in the sealed envelope auctions, subjects were inclined to bid lower for bags where they knew the number of chocolates inside. This is because the participants were already thinking about the final result, as there was no real process in the auction in which they could invest effort, time and money.

In the fourth experiment, which also consisted of participating in an auction, but with different methods, it was tested whether uncertainty generated a positive experience, thus increasing motivation. Again, the uncertain reward attracted higher bids and the subjects rated the uncertain-reward auctions more positively.

Suggestions for future studies

In the conclusion of this study, the researchers focus on other factors that might influence motivation, inviting academics to research them more thoroughly.

For example, this effect might occur more in tedious tasks than in interesting and engaging tasks, because tedious tasks might benefit more from the excitement generated by uncertainty. Or it might occur less if the value of the reward is very high: subjects’ attention might shift from the process to the outcome very easily.

In any case, if you want to convince someone to do something for you, offer an uncertain reward.

Carlo Sordini


  1. Shen, Luxi & Fishbach, Ayelet & Hsee, Christopher. (2015). The Motivating-Uncertainty Effect: Uncertainty Increases Resource Investment in the Process of Reward Pursuit. Journal of Consumer Research. 41. 1301-1315. 10.1086/679418.
  2. Goldsmith K, Amir O. Can Uncertainty Improve Promotions? Journal of Marketing Research. 2010;47(6):1070-1077. doi:10.1509/jmkr.47.6.1070