The five-second rule surely owes its existence to the popularization of germ theory. People who abide by the rule must believe (at some level) that pathogenic microbes are tiny little beasties crawling about on the ground, with nothing better to do than to clamber onto dropped potato chips.
The truth of the matter is that in the ecosystem of the surface of a sidewalk, bacteria are (nearly) immobile sacs of cytoplasm, subject to the mechanical forces of wind, rain, and the feet of pedestrians. Some take the form of a nearly-crystallized endospore, a survival mechanism that will keep the organism safe through heat, cold, radiation, digestive enzymes, starvation, and dessication. As soon as the potato chip falls, the copious grease on its surface entraps these helpless bacteria (and some of the hardier viruses as well.)
But that's not what people visualize. Rather, they must have in mind animalcules, as described over three centuries ago by Anton van Leeuwenhoek: Tiny "animals" that may be seen only through a microscope of sufficient power. In the late 1800s, Robert Koch formalized the cause-and-effect model of pathogenic microbes, drawing on years of observations and research by himself and other scientists.
How interesting that popular science (the version of science that average people carry around and use to understand their world) recognizes the century-old germ theory just fine but has not progressed far beyond the animalcules of a third of a millennium ago.