Ch.6 SCARCITY: It's not uncommon for retailers to announce the lack of an item to fuel future desire for it. The idea is satirized in an old song that mimicked the cries of a local fruit vendor who called out, "Yes, we have no bananas. We have no bananas to-day." When my grandmother used to sing the lyric to me, I never understood the logic of the vendor's sales tactic. I do now. So, apparently, does Apple's phone division, which is infamous for undersupplying its stores on the day of a launch.

Ch.8 UNITY: Instructively, the closer the friendship (and the accompanying sense of unity), the stronger the influence of our friends' behaviors on our own. In a massive political-election experiment involving sixty-one million people, a Facebook message urging them to vote was most successful if it included photographs of Facebook friends who had already voted and, critically, one of the photos was of a close friend.

Ch.8 UNITY: "Macy's Fashion Director allows users to create an outfit and then collect opinions and votes from friends about buying the outfit. Using Fashion Director, Macy's was able to double its Facebook 'fans' to 1.8 million, and increase sales by 30% during the time it was launched. Levi's Friends Store creates personalized stores made up of items that friends like. The Store attracted more than 30,000 fans when it launched, and allowed Levi's to increase its social reach to over 9 million fans. The Friends Store has a 15% higher sales rate and a 50% higher average order value."

Ch.8 UNITY: "We" relationships are not those that allow people to say, "Oh, that person is like us." They are the ones that allow people to say, "Oh, that person is one of us." The unity rule of influence can thus be worded: People are inclined to say yes to someone they consider one of them. The experience of unity is not about simple similarities (although those can work, too, via the liking principle). It's about identities, shared identities. It's about tribe-like categories that individuals use to define themselves and their groups, such as race, ethnicity, nationality, and family, as well as political and religious affiliations.

Ch.7 COMMITMENT AND CONSISTENCY: Reminders of existing commitments possess yet another bo-nus. They not only restore the commitment but also appear to strengthen it by augmenting one's related self-image. Compared to consumers who had previously performed pro-environmental actions but were not reminded of them, those who did receive such reminders came to see themselves as more environmentally minded and then became uniquely more likely to purchase environmentally friendly versions of products—including light bulbs, paper towels, deodorants, and detergents. Thus, asking people to recall prior commitments to environmentalism isn't just an easy way to stimulate consistent subsequent responding; it is also a particularly effective way, because such reminders intensify one's self-image as an environmentalist.

Ch.7 COMMITMENT AND CONSISTENCY: I ran an experiment designed to get university students to agree to perform an unpleasant activity—to wake up very early to participate in a 7:00 a.m. study "on thinking processes." When calling one sample of students, we immediately informed them of the 7:00 a.m. starting time. Only 24 percent were willing to participate. However, when calling a second sample of students, we threw a low-ball. We first asked if they wanted to participate in a study of thinking processes, and after they responded—56 percent of them positively—we mentioned the 7:00 a.m. start time and gave them the chance to change their minds. None did. What's more, in keeping with their commitment to participate, 95 percent of the low-balled students did appear for the study at 7:00 a.m. as promised.