Completeness Effect
We often estimate how much we should consume of a product based on aspects of its physical shape. If a product looks incomplete, we’re likely to incorrectly see it as having less value and so consume more of it.
Related studies:
Sevilla & Kahn (2014) The Completeness Heuristic: Product Shape Completeness Influences Size Perceptions, Preference, and Consumption. Journal of Marketing Research.