What Bullet Holes in Airplanes Can Teach You About Making Better Business Decisions


I don't experience much cognitive dissonance these days, but the following story from a book I am reading (and will review later) slapped me upside the head. I'm normally very good with problems like this, so when I didn't immediately understand it, I was surprised. I'll pose the problem below, and make you click through for the answer.

During World War II, statistician Abraham Wald tried to determine where to add extra armor to airplanes. Based on the patterns of bullet holes in returning airplanes, he suggested that the parts not hit should be protected with extra armor. Why?

Wald was looking at what is sometimes called "dead evidence." He reasoned like this… if these planes are returning, we know that if they are hit in the spots they have been hit, they can still fly. The planes that did not return must have been hit in different places. So put the extra armor wherever the returning planes were not hit.

I think most people would have a natural inclination to put the armor where the returning planes had been hit. The real answer is simple, but counterintuitive. It's called "dead evidence" because it is what people ignore when they make these judgments. For instance, you may see a story on tv about how to survive a plane crash. The producers will interview 10 plane crash survivors, and figure out what they did in common, then recommend that you do that too. What they don't think about is how many people did those same things, but still died in the crash. The dead can't be interviewed, so we will never know.

How can you use this in your business? Think about the dead evidence. Don't look just at winners, look at losers to see if they did the same things as the winners. Don't just look at what the top companies in your industry are doing, look at what all kinds of different companies are doing. Sometimes you can learn more by looking at failures than at successes.

  • Nice article – I never thought about data and metrics in quite that way!

  • Hi Rob,

    I got that one in a couple seconds. I guess even a blind squirrel finds an acorn now and then…it’s that or the benefit of my old product troubleshooting days!


  • It was an interesting and insightful example. i did thought what solution said, but wasn’t so sure.
    wud like to know the name of the book the author said in the beginning.

  • Sergey

    This is true but painfully hard to put in simple words when explaining to someone. People have such a strong urge to copy others that it’s hard arguing that some advice has not enough evidence of being good even if it’s coming from successful people. Just one solution comes to mind — leave them alone and do it right yourself.

  • Fred

    This is from operations research. It seems counterintuitive only if your intuition is bad. Please don’t vote or operate heavy machinery while under the influence of bottled water.

  • I had this reasoning, enemy firing might have some idea where they are targeting and missing, thus put armor where not hit.


  • Of course, adding extra armor may cause the planes to fly slower, making them more likely to be hit in the first place. Which just goes to show, just because you figure out one problem doesn’t mean you are out of the woods! Continuous testing and incremental improvement is usually the best strategy…

  • Very interesting article Rob. I certainly would have never figured that one out without a lot of thought. Thanks for expanding my thinking today!

  • That’s an awesome post. I just learnt another good lesson in my new endeavor with the business world. Thanks

  • Really intriuging thought! Thanks for sharing.

  • Its really nice and deep exploration of how our mind works.Keep it up…

  • Many things can be learned from how some things are built. Even more can be learned by taking careful note of how they are taken apart, like what is shown in the link. What business insights can be gained from this documentation? http://www.thenewsroom.com/details/460833/US?c_id=wom-bc-ar

    – Alvin from The U.S. Desk at TheNewsRoom.com

  • What a great way of looking at things. Like the average person, I would have been shoring up the parts of the plane that got hit, thinking it’s a sign of the most-targeted areas, or something.

  • Interesting – it took me a few moments to realise why and then a few more to really appreciate the implications of it. I think I’ll be sharing this with colleagues!