Jean Piaget developed a model for children's intellectual development. One of the milestones is the understanding that a liquid doesn't change its volume when it's poured from one container to another of different shape. This is known as conservation. However, sometimes it's painfully obvious that this is an understanding on a more superficial and intellectual level, as when a friend poured the contents of a can into a glass with seemingly larger diameter yet the water level ending up much higher in the glass. We could figure out that the thickness of the walls of the glass was larger than those of the can, yet the effect was eerie.