We all do it — don't even try to deny it.
The rule assumes that if food only touches the ground for a few seconds, it hasn't even picked up enough germs to be inedible.
Here's the thing: Food instantly picks up all the germs from the ground wherever it falls. So the rule is pretty much bogus.
What matters most is where you drop the food and what kind of bacteria or viruses are hanging out there.
If the ground is contaminated with a pathogen (germs that cause infection), food that touches the ground will get contaminated too. Obviously, this risk varies depending on the floor — a meatpacking plant is much worse than a bedroom. But carpets can be particularly grimy, since the bacteria there are harder to remove. And any high-traffic area is especially bad, since all sorts of stuff can be tracked around by people and animals.
Fun fact: Almost all indoor floors contain fecal organisms, Gerba says, which get tracked in on your shoes from the bathroom. So yeah, there's usually poop and diarrhea on the ground. And it can contain infectious bacteria like E. coli or salmonella if the poop comes from a sick person.