Always name the specific thing you are giving up

When you say yes to something, say explicitly what you are saying no to.

Why it works

The opportunity cost is invisible by default because it is the counterfactual — the path not taken. Behavioral research by Frederick, Novemsky & colleagues found that people who were reminded to consider what they could do with the money were significantly less likely to make a purchase, demonstrating that opportunity costs only influence decisions when they are explicitly activated. Naming the foregone alternative is the activation.

How to do it

1. Before committing to any significant use of time or money, ask: "What is the single best thing I would do with this instead?"
2. State that alternative explicitly — not as a vague "other things" but as a concrete activity or purchase.
3. Compare the value of the chosen option to the value of the named alternative, not to zero.
4. Use this check routinely for commitments of more than an hour of time or a meaningful amount of money.

Evidence

Frederick et al. (2009) found that prompting people to consider opportunity costs significantly shifted their purchasing decisions, providing direct experimental evidence that explicit opportunity cost consideration changes behavior. (rct)

The effect was demonstrated in consumer purchasing contexts; generalization to time allocation decisions is mechanistically sound but less directly tested.

Sources

• Frederick, Novemsky, Wang, Dhar & Nowlis (2009), opportunity cost neglect, Journal of Consumer Research

Common mistake

Comparing the new option only to "not doing it" (net gain = value of option minus zero), rather than to the next best use of the same resource.