The Element of Surprise

Surprise is not a word that user interface designers typically like to hear. Indeed, the principle of least surprise (also called the principle of least astonishment) is that systems should always strive to act in a way that least surprises the user.

Like many interface design principles, the principle of least surprise reflects the premise that software applications exist to be useful. In utility-oriented applications, surprise means distraction and delay — negatives that good designers work to avoid.

But we increasingly see applications whose main value to the user is not utility, but entertainment. Indeed, a recent Nielsen report claims that the top two online activities for Americans are social networks / blogs and games. I take the report with a grain of salt, but it seems safe to argue that people have come to expect the internet to be at least as fun as it is useful.

Even search, which would seem to be the poster child for the utility of online services, is being pressed into the service of entertainment. Max Wilson and David Elsweiler argued as much in their HCIR 2010 presentation about “casual leisure searching“. They mined Twitter to analyze a variety of scenarios where search isn’t about the use finding something, but rather about enjoying the experience. Indeed, their controversial definition of search is broad enough to include the possibility that the user does not have an information need.

Like the businessman in Antoine de St. Exupery’s Le Petit Prince, I’ve long felt that, as “un homme sérieux”, my job is delivering utility to users. Users already have lots of ways to waste time; I focus on making their productivity-oriented time more effective and efficient. I’m glad there are folks who devote their lives to making the rest of us have more fun (especially all the computer scientists who left academia for Pixar), but entertainment simply isn’t a vocation for me.

However, I’ve been coming around to the realization that fun and utility are not mutually exclusive. For example, news serves the utilitarian ideal of informing the citizenry, but many (most?) of us read news as a pleasant way to pass the time. Social networks are another example serving a similar function–perhaps with a balance that is more toward the entertainment of the spectrum but still providing genuine social utility.

A common feature of both of these examples is that users regularly return to the same site expecting the unexpected. The transient nature of news and social news feeds promises an endless supply of fresh content, produced more quickly than users can consume it. This situation is in stark contrast to those of typical web search queries, for which the results are expected to be largely static. Indeed, we may set up alerts to inform us of novel search results, but we are unlikely to regularly visit a bookmarked search results page the way we regularly visit a news or social network site.

Is novelty the only source of surprise? Novelty certainly helps, but it is not a necessity. An alternative source is randomness. I’m known people to use Wikipedia’s “random article” feature. But a more plausible place to introduce randomness is in recommendations — whether for products or content. Since recommendations are good guesses at best, a bit of randomness can help ensure that the guesses are interesting. Indeed, a SIGIR 2010 paper by Neal Lathia, Stephen Hailes, Licia Capra, and Xavier Amatriain on “Temporal Diversity in Recommender Systems” explored the use or randomness to induce diversity in recommendations and arrived at the conclusion that people don’t like being recommended the same things over and over again.

Can we generalize from these examples? I think so. For utility-oriented information needs, it is important to provide users with accurate, predictable, and efficient tools. But we can’t dismiss everything else as frivolous. Sometimes we just need to offer our users a little bit of surprise to keep it interesting.

Or, as Mary Poppins tells us: “In every job that must be done, there is an element of fun. You find the fun, and – SNAP – the job’s a game!”

By Daniel Tunkelang

High-Class Consultant.

9 replies on “The Element of Surprise”

Absolutely, you can definitely get people to do work by making it fun. A great example of that is the GWAP work by Luis von Ahn.

This is also a way to fix problems with usability and adoption of a product that people find requires too much effort. If you can make it more fun, more people will put in the effort.

There was a great talk on this a while back. The speaker was talking about how to integrate ideas from games into web design to make your site more fun. Let’s see, oh, here we go, this is a summary of the talk:


Greg, I meant to weave GWAP into this post but didn’t get around to it — so thanks for bringing it up! As I see it GWAP is about using fun as a motive to inspire users to deliver productivity to others. In contrast, I’m thinking about situations where the user experiences both the fun and the utility. Of course, we should do both!

Thanks for the game mechanics link. The discussion about feedback seems to be along similar lines to my feelings about the role of surprise to build user engagement.


Hi Daniel,

Thank you for once again mentioning our work. I think to focus on fun would be too narrow. Like you I think the motivation behind my research is to make people more efficient. However, with the casual-leisure work we discovered that efficient is not always what people want. I think what we are learning is that the key point in both work and play scenarios is “user experience”. The ideal experience in these situations may not be the same, but it is important that as system designers we get this aspect right. Doing this requires more work to learn about what makes the right user experience in different situations. But you are right, the aspect of surprise could very well be important.



A really interesting topic with many areas to talk about. Here is a lowball: “Users already have lots of ways to waste time”. I’d say that in an always connected world that people do have lots of ways to waste time but people don’t want to knowingly know they are wasting time or want to waste time. They’d rather waste time efficiently. For example, if I’m waiting on a platform for the train to arrive in 7 minutes, there are many options including doing nothing, reading a paper or book (unlikely options if you’re a teenager), playing a game on my mobile device or checking into FB. The 7 minutes were available to waste but I would like to fill it efficiently with things that I would like.


David, point taken — I may be trying to be a bit too clever by emphasizing fun / surprise rather than user experience more broadly. My main goal was to question my own preconception that utility and entertainment are mutually exclusive.

Dinesh, I think we’re on the same page. Wasting time efficiently = obtaining utility entertainingly. Or something like that.


Hi Daniel,
Thanks for the interesting post. Your example of integrating randomness into the recommnedation process reminds me a different aspect of it – in model based learning a standard technique to improve the current user model is to explore his/her preferences by suggesting sub-optimal items, but with high potential for exploring the user’s hidden preferences. Reinforcement learning provides a nice framework to the exploration vs. exploitation trade-off during model acquisition. I believe that “surprise” can be interpreted in that framework as the exploratory actions the system takes for learning the user. Thus, surprising the customer with recommendation of non expected items is not just for entertainment – it allows the system to actually explore the user preferences for better interaction in the future.


Let me just add that what David says is kinda where I was trying to point with my comments from a week or so ago, when I was trying to discriminate between faceted search and exploratory search. To me, exploratory search is much more of a process than an outcome. Certain interfaces make the process easier than others. And certain algorithms do or don’t support that process. But at the end of the day, what makes search exploratory search is it’s process orientation, not it’s outcome orientation.


David, that’s a good point — randomness is a great way to introduce perturbation and thus obtain more signal about the user’s preferences.

And Jeremy, point taken. Certainly the notion of exploratory search that Max Wilson and David Elsweiler put forth is quite different from those I usually associated with faceted search.


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