Opportunity Cost
Also called: economic cost, next best alternative
Opportunity cost is the value of the best thing you gave up to do what you did. It's the reason accounting profit and economic profit differ: a business owner who pays themselves nothing still bears the cost of the salary they could have earned elsewhere. In investing it's the discount rate — capital committed to one project cannot earn the return of another, which is why 'we already own the building' is never a reason to call space free.
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