My daughter asked why I always buy the family-size cereal but we run out by Wednesday

I explained it's all about optimistic volume planning.

I stand in the cereal aisle, see that big beautiful box, and think, "Yes. This will last us two weeks, easily." I picture leisurely breakfasts, reasonable servings, maybe even some left over for a sensible snack.

Then Tuesday night I find someone eating it dry by the fistful while watching cartoons.

Punchline

Family-size just means we all get to be disappointed together when it's gone.