The temptation not to waste food.
There I was, slightly full, a bit overweight, and in front of me a quarter of a luvvverrly pizza. It was practically screaming: "Eat Me!" Nobody else in the restaurant wanted it. It would be a waste not to eat it.
But when we ordered too much food we'd already wasted it. If I ate that bit of pizza I would be contributing to my own over-weight , the fuel consumption of my car, the fuel consumption of any planes or trains I took, and the average health of the nation would go down.
Once too much food has been prepared, and if it cannot be saved for later, the waste has already happened. It is an excuse for me to say "I hate waste!" and then add to my own belly fat. I have to throw the food away, that is the less wasteful option. (Unless of course I am undernourished. But I'm not.)