Why Do Designs Fail?


With so many scientific tools, why do designs fail?

Why the unsinkable Titanic sank? Why did the thoroughly tested Columbia space shuttle burned out on return? Why Toyota had to call back thousands of cars designed by expert engineers?

Design might fails because somebody made a stupid mistake in his calculations, like in the old joke about the bridge that fell down because the engineer forgot to multiply by two. It might happen, but it is extremely rare. Most design failures happen because one specific mode of failure was never checked against, because it was never identified as risky.

The sad truth is that we cannot design anything to work. We can only try to find out if a certain design might fail in a certain specific way. This is one reason why we cannot send computers to design things. They are excellent in optimizations, when we tell them what parameter to optimize and for what mode of failure.

The Tacoma narrows bridge collapsed in 1940 because nobody thought that wind might arouse resonant vibrations in the bridge. It was OK for what it was designed for: for static loads. No computer would have suggested another mode of failure.

The Titanic sank because nobody asked what happens if the ship scratch its side on an iceberg. Had it been thought, maybe the designers would have ordered that it would be better to throw the engines to full back and bump into the iceberg head on! It would have been damaged badly, but it would not sink.

If only the designers of the Columbia would have only thought of the possibility of losing their thermal shield bricks on launch, the Columbia would have still be in service today. For a fact, once they identified the problem, they had no big difficulty to fix it.

The philosopher of science, Karl Popper, said that in order to be scientific a claim must be “falsifiable”. Moreover, he suggested that a claim cannot be proved by repeating experiments with positive results. No matter how many times it passes a test, there is always a chance that one more test will prove it wrong. To prove a theory requires infinite number of successful tests. One failure is enough to disprove it.

So it is in our world of design. The failures described, all have shown that these designs were not perfect. They had errors embedded in them. And these errors are all the result of not being able to foresee the single mode of failure that could go wrong. No scientific calculation can help against an unidentified mode of failure.

What is the lesson to be learned? Be paranoid! Always look around searching for the mode of failure you might have missed.

I like to call rules by names. The name I gave this rule is “the law of the wild west”.

It goes as follows:

The guy who kills you will be the one hiding behind the bush, that you failed to notice!

About: Adam Rubinstein

Born in Israel, studied Mechanical engineering in the Technion, specialized in mechanical design and particularly mechano-optics. Over 50 years experience as a design engineer, and about 24 of them as an independent consultant. lately, partially retired and teaching mechano-optical design at BGU in Beer-Sheva, Israel. Interested in photography and classical choir singing

10 Responses to Why Do Designs Fail?

  1. le tant says:

    It is an excellent article
    And please let me add another cause of failure ( Over confident )
    I belive that if the person is over confident, he will make alot of mistakes.
    Because when you think what you did is perfect you forget alot of mistakes.
    And may be the failure is a sky punishment for people make mistakes.

    Thank you for your listenning

    • Wilbri says:

      I agree with you.To me a display of overconfidence displays arrogance which displays immature ignorance, a sense of pride.Now according to an old English saying: "Pride comes before the Fall".

  2. Mugeshkannan says:

    Is that is the only reason???????? I don’t think so there are many more like using a machine or toll of less accuracy and Like past comment overconfident

  3. DScullion says:

    I understand where you are coming from, basically for any failure in the field (regardless of root cause), if it had been (or could have been) predicted, it would most likely have been avoided.

    I am nervous however as the suggestion given is that it comes down to luck and I am surprised not to see the term ‘risk’ or ‘risk management’ used anywhere. Failure Mode and Effect Analysis (FMEA) is a great tool to use to predict failure modes up to an acceptable level of risk.

    Also, that acceptable level of risk is very often a commercial factor – if you make something idiot proof, someone will just make a better idiot. There is only so much risk you can be expected to manage and infact, failure modes are often designed into products for example your car tyres are designed to wear out and need replaced

  4. Gary152 says:

    Like for Failure Mode and Effect Analysis (FMEA)

  5. Zardiw says:

    Well, the Titanic sank NOT because of design defects but because it hit the mother of all icebergs.

    Also Pilot Error had a lot to do with it, they tried to stop, but what they should have done is put the propellers on one side into full reverse and the other into full forward…….so they would have pivoted away from the berg.

    And the Space Shuttle? …….Again that was NOT a design defect. It was POLITICAL. Engineers involved warned that the temperature was too low and that it would cause the O Rings to be too hard to effectively do their DESIGNED function.

    BUT, the all powerful and knowing reagan who was president, urged them to launch anyway…….

    True Story.


  6. Zardiw says:

    Not to mention that the Titanic was going way too fast for conditions……again a HUMAN error/Political mistake.


  7. Zardiw says:

    This is a ridiculous statement…….in fact the entire premise of this post is flawed……:

    The sad truth is that we cannot design anything to work. We can only try to find out if a certain design might fail in a certain specific way. This is one reason why we cannot send computers to design things. They are excellent in optimizations, when we tell them what parameter to optimize and for what mode of failure.

    Of course we can design MANY things so they will not fail………and Computers are invaluable in calculating various factors of the design and optimizing such.


  8. JDavid says:

    I have to agree with Zardiw here.

    It is impossible to find every possible way that something might fail under normal operation… let alone once you add an operator to the mix.

    I agree as well with the FMEA and Risk management. You can never stop thinking about ways that something might fail, but it gets to a point where you are just wasting time.

    There was an over site on the Titanic of the steel strength in salt water, but that alone didn’t sink it. There was a host of other things that have been mentioned.

    An oversight or flaw in the design is a possible reason for a failure, more often then not if there is a human involved it will be because of human error.

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