This article was originally published in UX Magazine on September 23, 2010.

Read part 1 of the article.

Using Scarcity to Encourage Participation

There's another twist on scarcity, one that may seem contrary to everything stated so far. This twist is one of creating artificial limits—specifically, character limits. By enforcing a scarcity of characters, you can actually encourage participation (this is different from creating desire as with the examples above). Twitter is the perfect example of this.

The technical limits of mobile text messaging were the original constraint behind Twitter's 140–character limit. But it is precisely this character limit that has driven a new form of written expression. Prior to Twitter, there were blogging tools such as Blogger, Wordpress, and SixApart. Anyone could certainly have written short, 1–2 sentence blog posts. But we didn't. I would have never written a blog post about eating my last piece of Leonidas chocolate, but I can certainly tweet about that. It's this character limit that allows people to be more casual about what they write—after all, it's only 140 characters! It's okay to say less, speak informally, or make typos in such brief messages; this isn't an essay paper, after all. The context lowers the bar on what can be "published" on the Web. It's liberating to have none of the expectations inherent in other forms of written communication.

To be clear, this is a very different kind of scarcity than if you were allowed say only one tweet per week. If this were the case, we might see much more thoughtful 140-character exclamations. But the character limit has made it much easier to post (and, in doing so, lowered expectations). Tweets are unlimited, more like words in a conversation. Why? Because a tweet can't exceed 140 characters. By making this number so low, Twitter is essentially saying, "It's easy, what's stopping you?" Scarcity encourages participation, by making it that much easier to join in.

Rypple uses this same insight to make feedback and coaching easy. With Rypple, users can request peer reviews to help them get better at their jobs. If you want candid feedback on that presentation you just gave or your management skills, Rypple creates a safe environment to solicit and give such critiques. Co-founder Daniel Debow observed that "the most senior people tend to send very brief emails." While people would like to give feedback to others, there isn't always the time to do so. By limiting comments to 400 characters, the "cost [in terms of time] to the reviewer is much lower, especially in contrast to long surveys and other corporate tools.

Rypple feedback

A limit on characters lowers the expectations associated with offering feedback.

This number, along with other variables, has been iteratively tested over the past year. Rypple wants to encourage people to respond, and to do this the team has tested limits as low as 120 characters. However, they also want to leave enough room for constructive feedback, so the team has tested much higher limits. 400 characters seems to strike the best balance between increasing the number of responses while still allowing for substantive feedback. Debow also adds that "when you encourage and design for brevity, you also encourage people focus their feedback."

This idea of using scarcity to increase participation isn't limited to characters. What if email inboxes could only receive 15 mail items at a time before they were literally full? Would that encourage us to clean out our inboxes? Or what if a signup form allowed users to list only three of their favorite movies in a signup form? Would that limit be less intimidating to complete than a big, empty textbox?

Why Does Scarcity Work?

One explanation of why scarcity works so well on us has to do with decision-making. It's easier to "go along with the crowd" and buy the thing that is scarce. Why? According to persuasion expert Robert Cialdini, things "that are difficult to possess are typically better than those that are easy to possess." (Influence: The Psychology of Persuasion, 1998). People use this defining attribute—limited availability—to aid in their decision-making processes. If a bakery is running low on one kind of pastry but has plenty of the alternatives, that might be a good indication of what is popular (and what's to be avoided!). Scarcity is often a shortcut to the best choice.

This helps explain scarcity as a selling tactic, and possibly why character limits might help people choose a restrictive format over an open-ended one that offers no constraints. But what about the kind of scarcity (as with Foodspotting or Dribbble) that improves quality?

Another explanation of why scarcity works has to do with freedom—or rather loss of freedom. If something is scarce, it may be unavailable in the near future. And that idea doesn't sit too well with people—it violates our sense of control over a situation: "If I don't act today, I won't be able to…" Psychologist Jack Brehm writes about "psychological reactance," or the ways people fight against restrictions on their freedom. Brehm explains why teenagers who are only mildly interested in each other will continue dating as a protest to their parents disapproval, or why people rush to protest government restrictions on their rights, even when the issue means very little to them personally. Scarcity of something is essentially a threat to freedom of choice. But this threat isn't necessarily a bad thing; it can be a useful means of encouraging desirable user behaviors.

Scarcity and UX

While the aim of this article has been to suggest creative ways to use scarcity, this idea shouldn't be used to the detriment of your users. Scarcity is a powerful persuasive tactic, one that's frequently used in sales. Whether people feel pressured or pleased depends on how scarcity is applied. Customers might feel regret after purchasing something they didn't really want. But they might also feel relieved to have made the right choice or to have gained something exclusive. Scarcity has value beyond being a sales tactic; it can encourage participation and quality as well. Many games create a thrill by making something scarce. Imagine Monopoly with unlimited cash or any arcade game with unlimited lives. Yes, there's certainly a pressure that's coupled with scarcity. But it's the kind of pressure that creates a appropriate level of anxiety, which can actually make things more fun, playful and exciting. Scarcity is a useful psychological tool that can be applied to software and web design in many creative, constructive ways. We can cause people to value something more by introducing simple economics into our designs.

Learn More on Scarcity and Seductive Interactions

You can learn about many of the other techniques in Stephen's upcoming UIE Virtual Seminar, Leveraging Seductive Interaction Design. During this Thursday's 90-minute seminar, he'll walk your team through some great examples of how you can open up your design's value and functionality to your users. Don't miss it. Get the details on Stephen's webinar.

Share Your Thoughts with Us

What techniques for persuasion do you love about the sites you visit? What have you tried in your own designs? Share your thoughts at the UIE Brain Sparks blog.

 Share this article with a friend/colleague.

Subscribe to UIEtips, our free email newsletter


  • Awesome UX insights delivered to your inbox
  • Access to our incredible content library
  • Podcasts that help to improve your UX skills
  • Learn about our in-depth live events