System Architecture Principle 3: What can go wrong will go wrong

Tagline: What can go wrong will go wrong.

Descriptive version: It is very rare for a system of greater than medium complexity to operate without failure. This applies to both the satisfying the intended needs and anticipating future needs.

Prescriptive version: Robust design, flexibility in design, and design for contingency and emergency operations are critical to the success of a system.

Discussion: The potential history of this ``law'' dates back to an 1877 meeting of the Institution of Civil Engineers (Holt1878):

It is found that anything that can go wrong at sea generally does go wrong sooner or later...

Various other written references to the law of turned up over time, including in the context of stage magic, mountaineering, and as a name for the second law of thermodynamics. The law has been attributed to Capt. Ed Murphy, and engineer from Wright Field Aircraft Lab (Bloch1977), and to an unnamed theoretical physicist (possibly from California Institute of Technology, aka "The Other Technical School"). While it is difficult to pinpoint its origins, the law quickly spread throughout various aerospace engineering cultures (Unknown), into the engineering and science communities, and eventually into popular culture.

In the context of systems architecture, it is important that one consider all possibilities in the design and implementation of the system. Tools and techniques to do this include the consideration for contingency and emergency operations, designs that are robust to variability in operating conditions, to consider flexibility in design so a system can accommodate future unanticipated needs and operating scenarios. This should also be expanded to include consideration of human factors; humans are unpredictable, messy system elements and all care must be taken in the design and operation of systems that require humans to execute any of the system functions.

Citations

A. Holt. Review of the progress of steam shipping during the last quarter of a century. Minutes of Proceedings of the Institution of Civil Engineers, LI:2{10, 1878.

A. Bloch. Murphy's Law, and Other Reasons Why Things Go WRONG. Methuen Paperbacks Ltd, 1977.

Unknown. http://www.catb.org/jargon/html/M/Murphys-Law.html.