Everyone's had firsts. Everyone's had seconds. And there is still one piece of food on the plate. That no one will touch.
Paulette, Fab's mother, called that "Le morceau de la vergogne" -- the piece of shame. You shame yourself by taking it. Your essentially anti-social and selfish nature is on display if you eat the last piece. And therein crouches today's paradox. After all, it's food. It's meant to be eaten. Yet no one dares touch it.
The solution? Announcing that the piece will be discarded, hence "wasted." Then someone will say, "Oh, well, it shouldn't go to waste. I'll take it." Shame converts to public service.