Franklin compares love with a cough and smoke because all three tend to reveal their presence even when someone tries to conceal them. A cough produces an involuntary sound, while smoke becomes visible; similarly, strong affection may show itself through attention, behaviour, expression or changes in manner.

The saying does not suggest that every feeling of love is obvious or that observers can always interpret another person’s behaviour correctly. Its point is more general: powerful emotions are difficult to keep entirely private because they influence how people act. Franklin’s comparison gives this idea a humorous, everyday form. The broader lesson is that inner feelings often produce outward signs, and attempts at concealment may therefore be less successful than the person experiencing those feelings expects.