Economists use models of human behaviour that incorporate such non-human features as complete rationality and perfect information. Psychologists should not fall into a similar trap.

Peter Todd's article contrasts findings on shoppers' preferences for the products they know with their more exploratory behaviour in money-based laboratory experiments (see Nature 541, 294–295; 2017). The assumption in interpreting such results seems to be that consumers aim to 'optimize' the products they buy. But unless an optimal product is defined, this hypothesis is untestable because it is subjective.

Apart from perishable produce, I for one do not care about optimality. I care only about adequacy: whether an item meets my needs and is available and affordable. Once these criteria are satisfied, I need never look again. What are the chances that a new shampoo will be so much better as to be worth trying, given that my current one is adequate?

Todd's bear-foraging analogy for consumer choices therefore seems misleading. Bears presumably leave a berry patch when there is insufficient food, not because they want to find more-optimal berries. If brands appeared and disappeared like berry patches, then consumers might have to adopt a foraging strategy to sample new shampoos as they came into season.