When did we become afraid of eating off the floor?

Maybe this is a cultural thing, but the idea of a solid food hitting the floor and it suddenly being off-limits is alien to me. I was taking a pill for pain this morning. I dropped it on the floor and picked it up and swallowed it with water anyways, and a classmate I was with had this reaction like I had just eaten a worm. Does it supposedly cause illness or bad luck, because I've never gotten any in all my years...