The last donut

That, my friends is a donut. It's covered in powdered sugar and filled with chocolate creme. There's no hole in the center but I assure you, it is indeed a donut. As such, there's no question it is delicious. Because it's a donut. It's delicious-ness is inherent. Yet, no one will ever eat that donut. Nobody will ever even touch it. Not because there's anything wrong with it, but because it's the last donut.
There were once many donuts in that box. Dozens! Over the course of time (this morning, in the office), people visited this box of donuts, which was at one time, full. People came by, sometimes one-by-one, other times in small groups, and they would each take a donut to enjoy. They would make these individual selections based entirely upon their own personal preferences. For no good, less-arbitrary reason than that, all the other donuts were selected before this one. It became, through no fault of its own, the last donut.
After this, people still came by to look at the donut box. Some of them were people who had previously selected a donut and thought about treating themselves to a second donut. They changed their mind when they saw that the only thing left in the box was the last donut.
Why, exactly, is this true? Why is there stigma attached to a donut based entirely on it's status as being the last one? Because it's actually less of a stigma against the donut than it is against the person who might take it...

"Oh look, who took the last donut. You couldn't resist, could you? Had to eat it. Just had to!!"
"Huh? No! I just got here and I didn't have time for breakfast and I saw the donut box and..."
"Liar! I parked next to you this morning. You filthy, lying scavenger!"
"B-but what's wrong with eating it...?"
"You're a pig, that's what's wrong. Nobody else felt it necessary to finish off that box of donuts. But you sure did."
"Hey! It's not like I ate all the donuts. I just happened to have the last one."
"Oh, shut up, reviled eater of the last donut. Your very existence disgusts us."

As though eating an entire box of donuts except for one demonstrates an admirable level of restraint and moderation. How silly. Still, nobody wants to be the office pariah. So instead, for the sake of nothing more than a false sense of shallow, human pride, somebody had to throw this poor, innocent, delicious donut in the trash.
Yeah, that's probably what happened to it.