Murphy's law

Whatever can go wrong will go wrong. So a solution is better the fewer possibilities there are for something to go wrong.


Systems are built and used by humans. And humans inevitably make mistakes. So if a mistake is possible, eventually, it will occur.

As mistakes are undesirable - you should design a system in a way that reduces them. The fewer possibilities there are to make mistakes, the fewer there will be and a greater chance of producing higher-quality software.

This also applies to system design, implementation, verification, maintenance, and use. Because all these tasks are (partly) carried out by humans.


Although often cited as a fatalistic comment, Murphy's Law is not stating "that life is unfair". Instead, it is (or at least can be seen as) engineering advice to design everything in a way that avoids incorrect usage. The Law applies to everything engineered, including all kinds of modules, [user] interfaces, and systems.

Ideally, incorrect usage should be impossible. For example, this is the case when the compiler will stop when detecting a mistake. And in the case of user interface design, a design is better when the user cannot make incorrect inputs as the given controls won't let them.

It is not always possible to design a system without mistakes. But as humans build and use systems, one should strive for such "fool-proof" designs.

Note that Murphy's Law also applies to every chunk of code. According to the Law, the programmer will make mistakes while implementing the system. So it is better to implement a simple design, as this will have fewer possibilities to make implementation mistakes. Furthermore, bug fixes will be necessary as current functionality is changed or enhanced as code is maintained. A design is better the fewer possibilities there are to introduce faults while doing maintenance work.


This is a very general principle, so there is a large variety of possible strategies to adhere more to this principle, mainly depending on the given design problem:

  • Make use of static typing so that the compiler will report faults
  • Make the design simple, so there will be fewer implementation defects
  • Use automatic testing to find defects
  • Avoid duplication and manual tasks, so you don't forget necessary changes.
  • Use polymorphism instead of repeated switch statements
  • Use consistent naming throughout the design


The exact wording and who exactly coined the term remains unknown. Nevertheless, it is stated that its origin is from an experiment with a rocket sled conducted by Edward A. Murphy and John Paul Stapp. During this experiment, a technician had wired some sensors incorrectly. Murphy - on recognizing the error - cursed the technician responsible and said, "If there is any way to do it wrong, he'll find it.". 1

Further reading

Derivative work

This work is a derivative of "Murphy's Law (ML)" by Christian Rehn, originally licensed under CC BY 4.0. The original version can be found here.