I was in line at the counter of a fast food restaurant this week. The young couple in front of me received their order and then went to sit down. When they left the counter, I noticed a car key (+fob) and other keys were on the counter. I quickly asked if these were their keys and they retrieved them.
This could have had a much different ending. They probably would not have missed the keys until they finished eating and then went to leave in their car.
Someone could have picked up the keys and easily found the car in the parking lot and taken it.
Never place your keys on the counter. Keep them on your person.