Opportunity Cost

Benefit, profit, or value of something that must be given up to acquire or achieve something else. Since every resource (land, money, time, etc.) can be put to alternative uses, every action, choice, or decision has an associated opportunity cost. Opportunity costs are fundamental costs in economics, and are used in computing cost benefit analysis of a project. Such costs, however, are not recorded in the account books but are recognized in decision making by computing the cash outlays and their resulting profit or loss.

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It's not effective for finance decisions only. It's the same like in our lives every day, the small and the big decisions we make... we always have to give up one, or a part of it to get another or a part of it. I only wish there was a formula to calculate how much exactly our gains and losses would be.