I think I should get a research grant to study this.
Why, oh WHY, will no one take the last piece of candy? Oh yes, I know you have your Momma's voice on tape in your head, just like I do: "Someone else might want that!"
But really, Mom. What about being wasteful?
Slice up a loaf of cranberry orange nut bread for your office break room. Those slices will disappear faster than a kid at chore time. All but that last slice. It will sit there and dry out, grow mold and finally develop a pulse before anyone will eat the last slice. Same thing for donuts or cookies or Tina's scrumptious lemon bars.
Fill a candy bowl at the reception desk. Customers will stuff their cheeks and their pockets, too, when the bowl is full. Leave one candy in it and no one will touch it. Well, to be more accurate, about half the customers will finger that candy while they replay Momma's voice in their head. Momma always seems to shame them into putting it back.
And why doesn't this theory hold true for the freebie pens? No one ever minds taking the last pen and casually remarking, "You're out of pens here."