Very. Brian Wansink, a professor at Cornell, has discovered that changing the size of a serving container for food increases consumption as much as 74 percent. A bigger bowl of stale popcorn: 53%. Want to double the number of potato chips someone eats? Make it hard for them to count how many they’ve had.
We still misunderestimate how irrational people are. Even students who had just been taught the facts in the paragraph above ate more than 50% more Chex mix when it was served from a bigger bowl.