D: On today's moment of science, we're going to talk about aspirin. Aspirin is a "pain-killer." They're called pain-killers because they make pain go away.
Y: That's not true. Aspirin doesn't work.
D: Whaddya mean, Yaël?
Y: Sorry. But you can't go telling people that aspirin works when I have personal experience that proves otherwise.
D: You do?
Y: Sure. My cousin Byron gets headaches all the time. He says aspirin never works for him.
D: So you assume it won't work for you either?
Y: Of course not! Listen, Byron is no liar.
D: Suppose I told you that ninety percent of the people who take a certain drug report that it works like a charm. Would you try that drug?
Y: (thinking): Well, I suppose so. Ninety percent seems pretty high.
D: Well, suppose I said that ninety percent of the people who use aspirin say it works?
Y: I told you, my cousin Byron...
D: Aha! So you'd be willing to ignore lots of compelling statistical evidence in favor of one anecdotal account.
Y: (puzzled): Well...I guess I did just say that...
D: You're not alone. Social psychologists are familiar with this effect, sometimes called "the man who" effect. I say: ninety percent of the people who try this drug receive benefit from it. You say "I know a man who tried it and nothing happened!" Somehow the face-to-face testimony of one person seems more convincing than any amount of statistics.
Y: Hmmm...I guess that's not very rational.
D: Nope. Because those statistics represent lots of individuals just like Byron.
Y: Well, nobody's quite like Byron. He makes a living pounding in nails with his forehead.
D: Well, that explains it...!