It sounds like such an incredible fact. “Our own cells are outnumbered by our microbes 10 to 1!” I don’t remember where I first heard it. But I read it in science papers and articles by journalists, so I believed it without question. I even made one of my first videos based on this fact. Problem is, this fact is not true. So how did it remain firmly planted in our common knowledge for almost four decades without any scientific scrutiny? And how can you prepare yourself to not be fooled by other scientific urban legends? I look at a few of the most famous incorrect factoids in science, and give a few suggestions for how to make our common knowledge more correct.