Strictly speaking, it would be difficult to make a case that the theory of the consumer conforms to our own experience of consumption decisions or what we observe of other consumers. We don’t consciously weigh the relative marginal utilities of tens of thousands of possible goods and services we might consume. We don’t know all the current prices and don’t even know of the existence of many goods and services. Even if we did, the computational complexity to solve for optimal consumption would overwhelm our faculties, and probably even the fastest computers available.
Many times we and others don’t think of our consumption in terms of what gives us the greatest satisfaction but in terms of what it takes to get by. Consumers who are impoverished or suffer a major ailment are probably unable to do even a modest attempt at optimizing consumption. Others may simply consume as a matter of habit rather than conscious choice.
Although our consumption decisions may not fully conform to the theory of the consumer, there have been some attempts to argue that we do approximate it. Herbert Simon proposed a theory of bounded rationality (bounded rationality and satisficing are discussed in Simon (1997)). that states that humans do behave rationally with a limited range of options. So if consumers focus on a modest set of important goods and services, they may be able to achieve something close to the theoretical optimum in terms of overall utility. Simon also observed that human beings may not optimize so much as they “satisfice,” meaning that they work to meet a certain level of consumption satisfaction rather than the very best pattern of consumption. If the level of acceptability is reasonably close to the optimum level, again the results of consumption decisions may approximate what would occur if the consumers operated according to this theory.
Another argument suggesting that differences between the theory and actual behavior may not result in starkly different consumption is that we observe how others behave. If someone else, either by active choice or by accidental discovery, is experiencing greater satisfaction under similar circumstances of wealth and income, their friends and neighbors will detect it and start to emulate their consumption patterns. So our consumption may evolve in the direction of the optimal pattern.
Perhaps most importantly, the lack of face validity of the theory of the consumer does mean the theory is not useful in modeling consumer behavior. We do expect consumers to respond to price changes and we do expect consumers to respond to changes in their wealth, whether due to changes in their actual discretionary income or indirect impacts on wealth resulting from price changes.