Amidst all the raunchy, rapid-fire silliness of Horrible Bosses 2, one joke is a perfect illustration of a common logical fallacy.
Much of the film’s humor derives from the fact that the three protagonists are incompetent criminals, with Nick (Jason Bateman) trying to keep Kurt (Jason Sudeikis) and Dale (Charlie Day) from goofing everything up. As Nick looks on while Kurt and Dale attempt to break into a building, the following exchange occurs:
Kurt/Dale: It’s a bust. It’s locked.
Nick: Your plan did not account for a locked door?
Kurt/Dale: Well, it’s a fifty-fifty chance it’s going to be open, right?
Nick: How do you figure that?
Kurt/Dale: It’s either locked or unlocked. Fifty-fifty. It’s like basic math.
In such a ridiculous scenario, it may be easy to see why Kurt and Dale are wrong, but the 50/50 fallacy is more common than you may think.
There are many situations where there are two possible outcomes and the odds of a particular outcome occurring are known to be fifty-fifty, such as a coin toss. In that case, identifying the odds as fifty-fifty is not a fallacy.
Also, in a different scenario, if you know that there are two possible outcomes, and you have no other information, it might be reasonable to guess that the odds of a particular outcome are fifty-fifty. The fallacy arises when we do have other information.
If you buy a lottery ticket, there are only two possible outcomes: you win or you lose. Most lottery players are aware that their odds of winning the jackpot are not fifty-fifty, but they may not realize how astronomical they are, and the fifty-fifty fallacy may subtly influence their understanding of the odds. There are only two possibilities: win or lose. Fifty-fifty. It’s like basic math.
The 50/50 fallacy can also affect people’s choices regarding snake oil cures, alternative medicine and self-help techniques. When presented with any given outlandish claim, say that balancing a glass of water on your head will cure your headache, we may feel that there is some chance that the cure will work, but we don’t know the odds. With two possible outcomes, we may imagine that the odds are somewhere close to fifty-fifty. Unable to properly estimate the odds of success, many people shrug and think, “No harm in trying. After all, there’s a chance it just might work.” Of course the harm comes when some unfortunate people with serious illnesses waste time and money on phony cures while neglecting real treatment.
A related problem is the balance fallacy, which occurs mostly in the media. Journalists are trained to report “both sides of the story,” and they often mistakenly give two sides equal weight. The issue of climate change is the most prominent example of this fallacy today. The two possibilities, that human activity is responsible for climate change, or that it is not, are not equally likely to be true, because an overwhelming international consensus of scientists supports the first position, and only a small number of scientists support the second position. Nonetheless, coverage in popular media, particularly in the United States, often gives equal weight to the two positions, fostering a perception among the public that each may be equally likely to be correct.