Scale is kind of important when comparing two things. By some measures, one human body is way smaller than the whole Earth. But by others, like the number of bacteria on the skin's surface versus the number of people on the planet, a person wins out.
BuzzFeed Video did some quick comparisons to show that our impact as individuals can be both infinitesimally small and incalculably (or in this case calculably) large. But don't get a big head, even if you do have a crap ton of neurons in there . . . [BuzzFeed Video]