Especially vaccines. It's such a counterintuitive concept : injecting yourself with a small doses of a disease to prevent that disease. Do you want some polio,

Especially vaccines. It's such a counterintuitive concept : injecting yourself with a small doses of a disease to prevent that disease. Do you want some polio, it's good for you? Er, no, go away you freak! Contrast that with atomic theory: nearly everybody can grasp the concept that bigger parts are made of smaller parts.