“Now, think of how you became good at it,” he says next. Audience members, supplied with wireless clickers, can choose from several alternatives: trial and error, apprenticeship, lectures, family and friends, practicing. Data from thousands of subjects make “two things stand out,” Mazur says. “The first is that there is a huge spike at practicing—around 60 percent of the people select ‘practicing.’” The other thing is that for many audiences, which often number in the hundreds, “there is absolutely zero percent for lectures. Nobody cites lectures.”