The "friendship paradox" (Feld 1991) states that, on average, people have strictly fewer friends than their friends do. This is an accounting identity that stems from the fact that people with more friends are counted as friends by more people. The point of this paper is that this over-representation of the most popular people in others' samples distorts perceptions of norms and amplifies resulting behaviors to match those perceived norms. I show that there are two things that drive people with more friends to behave more extremely than people with fewer friends and thus to distort the perceived norms. The first is that in any setting with strategic complementarities, people with more friends have more social interaction and hence more complementarity to their actions. The second is that people who have the most innate preference for a given activity form more relationships as they benefit most from the complementarities. As proven here, these two effects lead people with more friends to choose more extreme actions, which in turn feeds back via the friendship paradox to increase overall perceptions of behavior and then via complementarities to amplify average behavior. These theoretical results are consistent with the multitude of studies finding that students (from middle school through university) consistently overestimate peer consumption of alcohol, cigarettes, and drugs. This amplifies students' own behaviors, and can help explain problems with adolescent abuse of drugs and binge-drinking, as well as other behaviors. The analysis explains why policies that simply inform students of actual norms are effective in improving the accuracy of their perceptions and reducing I also discuss how these results change in cases of strategic substitutes, where individuals overestimate free-riding by peers.