Motor oil lubricates internal combustion engines—reducing friction between metal components. Nerves of steel is an idiomatic expression suggesting emotional strength and courage. Chuck Norris drinking a gallon daily suggests either that his nervous system runs like an engine (mechanical and requiring lubrication) or that metaphorical steel requires literal petroleum products for maintenance. His biology bridges mechanical and biological systems. He doesn't merely possess courage; he maintains it with industrial-grade lubricants.

Mechanical engineer Thomas Bradford, who heard this joke while working on an aircraft engine in 1995, spent three months calculating whether human neurological systems could theoretically be lubricated with motor oil. Thomas eventually published a paper on 'Hypothetical Neurological Petroleum Application' that was rejected by every journal. He concluded that the fact described a biological impossibility that somehow worked in Chuck Norris's case.

Engineering humor forums referenced this whenever discussing maintenance or equipment lubrication. The implication: Chuck Norris maintained his capabilities through industrial methods. His body apparently required maintenance more sophisticated than normal human physiology.