The Engineering Principle: If You Don't Know What You're Doing, Don't Do It

The engineering principle is most famously attributed to Richard Hamming, a legendary mathematician and computer scientist at Bell Labs.

He frequently contrasted the mindset of research versus engineering with this specific distinction:

“In science, if you know what you are doing, you should not be doing it.

In engineering, if you do not know what you are doing, you should not be doing it.”

This elegant formulation captures a fundamental difference between exploratory research (where the unknown is the destination) and engineering application (where predictability and safety are paramount).

Key Variations and Related Principles

While Hamming’s quote is the definitive on the “engineering principle”, several other thinkers have expressed similar sentiments:

The Fail-Safe Minimization Principle:

“If you don’t know what you’re doing, don’t do it on a large scale”.

This appears in Tom Gilb’s Principles of Software Engineering Management and is used to advocate for small, incremental testing when faced with uncertainty.

W. Edwards Deming:

“If you can’t describe what you are doing as a process, you don’t know what you’re doing”.

This focuses on the necessity of structured methodology in engineering to ensure predictability and safety.

The “Fit and Force” Rule: A common workshop adage often taught as the “First Rule of Engineering” is: “If it doesn’t fit, don’t force it”. This is a more literal application of “not starting” or continuing if the parameters aren’t correct.

Warren Buffett: Though from the finance world, he applies an engineering-style logic to risk:

“Risk comes from not knowing what you’re doing”.

He advises staying strictly within one’s “circle of competence.”

These principles all share a common thread: the recognition that competence boundaries are real, consequential, and should be respected in domains where mistakes carry significant costs.