Inadequacy turns a comparison into a judgment about the self.
People can compare their abilities, possessions, appearance, status, or progress with those of others. The comparison becomes inadequacy when the difference is interpreted as evidence that the self is deficient. Advertising makes this interpretation commercially useful by presenting an ideal, intensifying the gap, and attaching a product to the promise of repair.
The feeling is real, but its conclusion is not automatically true. A person may lack a skill or resource without being a lesser human being. When identity is tied to external comparison, however, every new image can become a fresh demand to buy, improve, display, or imitate.
Source: Festinger, L. (1954), “A Theory of Social Comparison Processes,” Human Relations.