John Stossel, 20/20 co-anchor and author of Myths, Lies and Downright Stupidity, tells Rachael why it's important to get to the truth behind myths. "We make stupid decisions when we have wrong information," he says. "I kept learning when I was reporting on things that half of what I thought was true was wrong."

Here are a few of the myths John debunks for Rachael:

• "Black Friday" is the busiest shopping day of the year. "The media says this all the time, but do we ever check it out? It's not true -- the weekends before Christmas earn much more money."

• Poinsettias are poisonous. "On one survey, most florists still believe that humans who eat poinsettia leaves will get sick. But even a toddler would have to eat like 500 leaves to get sick. It comes from 80-year-old myth of a soldier whose son died and they thought it was from eating the flower."

• Gas prices hit a record high this year. "This is another one where people in my profession were just economically idiots! It wasn't a record -- it's only a record when you don't adjust for inflation. And then you might as well say the movie Shrek 2 was one of the highest grossing movies of all time. If you adjust for inflation, gas prices were higher in 1920 and higher in 1980."

• Being cold gives you a cold. "They have studied this well. They've rolled people in the snow and injected cold viruses in their noses, and the people who were chilled got no more colds than anyone else. We think we get more colds when it's cold out because our noses run, and that we get more colds in the winter because we're inside more breathing on people and picking up their germs. It's not true, so you can relax!"

• Cracking your knuckles gives you arthritis. "People who study arthritis say no, it's just another myth. It's an air pocket that you're popping and it's just the noise. It's annoying, but not bad for you."

• Women are worse drivers than men. "Well, I think it's true [wink], but all the data shows that men drive more recklessly, speed more, are more likely to drive drunk, go through more stop signs, we kill many more people ... You can say it's because men drive more often, but even if you adjust for that, we're still much more dangerous on the road."