As an individual, it's easy to assume that there's not a lot you can do to affect change within a large group or an audience, but such an assumption is misleading. Look at Martin Luther. Look at his namesake, Martin Luther King Jr. Look at Hitler. Whether for good or for bad, these individuals have succeeded at calling large groups of people to action in completely radical ways.
People behave and react differently to things in groups than they do as individuals. A guy at a club with his buddies is almost always going to feel more confident and be more willing to try crazier things than the guy who came alone. By herself, you might never get the urge to take eight shots in rapid succession and then go make out with strangers and dance on tabletops, but with your friends, you sometimes turns into a party animal willing to take just about any suggestion thrown out there.
This book by author William Legend is about exploring the phenomenon of mass psychology and showing you how you can harness these powers to meet your own goals. It will give you detailed answers to questions like: How much power does an individual have over a group? Why and how do people conform? To what extent is behavior contagious? Do people always act in line with their beliefs?
The purpose of this book is to flesh out the answers to these questions and more in greater detail to show you how you can control, influence, manipulate, and persuade any group or audience.