Because it is counterintuitive until you understand what it is.
What is survivor bias? During World War II, the military wanted to add armor to the parts of returning bombers that showed the most bullet holes. An engineer told them to do the opposite. Why? The worst-hit planes never came back. All the data came from planes that made it to base. The spots with no damage were the worst places to be hit, because planes hit there didn’t return. Armor the engines and cockpit — the clean spots on the returning planes — because hits there were killing the planes that weren’t in the dataset.
Excerpt from You’re Doing It Wrong: Dump The Myths, Misconceptions, and Bad Advice You Believe.
A classic myth in survival is that drinking urine helps. Survivor bias in the urine-drinking myth works like this: we hear about the desert wanderer, the trapped climber, the lost soldier who drank their urine and lived. We don’t hear from the ones who drank their urine and died — they’re not telling stories. The sample is filtered by survival itself. (BTW– something I had wrong. Urine is NOT sterile. Do not use it on jellyfish bites or, really, anything else– covered elsewhere in You’re Doing It Wrong).
Worse, the survivors almost always survived despite the urine, not because of it. Aron Ralston, an entry in my Against All Odds book, drank his in Blue John Canyon; he was rescued shortly after self-amputating, and the ER physicians flagged the urine consumption as something that worsened his kidney status, not saved him. Mauro Prosperi did it in the Sahara during the 1994 Marathon des Sables — found nine days in, hospitalized in serious condition, and his doctors were clear that the urine and bat blood damaged him. Rescue saved him.
The bias compounds because the myth has narrative gravity. “He drank his own urine and lived” is a story. “He drank his own urine, died on day three, body recovered on day eleven” doesn’t get told — no protagonist left to tell it, and the family isn’t leading with that detail in the obituary.
There are a number of entries in You’re Doing It Wrong that go against what we think is common sense.
