Opportunity Cost

The value of the best alternative you give up when making a choice. Every decision has an opportunity cost—the road not taken. If you invest $100K in Project A, the opportunity cost is the return you would have earned from the best alternative use of that $100K. Opportunity cost applies equally to time, attention, relationships, and any scarce resource. The most important costs are often the ones you never see because you never considered the alternative.

Opportunity cost is the value of the best feasible alternative displaced by a choice, not the sum of every attractive possibility. Define the scarce resource and the decision margin: the next hour, an additional commitment, or money tied up for a year. An alternative that is inaccessible is not the relevant comparison.

Make comparisons using what happens from now onward. A past expenditure that cannot be recovered is not changed by the present choice, though future maintenance and resale value may matter. Benefits can include rest, relationships, or flexibility without being converted into dollars. The purpose is a clearer tradeoff, not an endless search for an imaginary perfect option.

When to use it

Every resource allocation decision. When evaluating whether to take on a project (what won't you do?). When time feels scarce (what are you giving up?). When a 'good' opportunity might be preventing a 'great' one.

How it can help

Forces explicit comparison of every investment against its best alternative. Prevents the common error of evaluating opportunities in isolation rather than relative to alternatives. The most fundamental concept in economic thinking and resource allocation.