CODEXCard 3 of 12 · 12 Mental Models
Opportunity cost
The price of yes is every no.
Opportunity cost is the idea that every choice has a hidden price: the best option you did not take. If you spend an evening on one project, the cost is not only the hours but what you would have gained from the next best use of them. The concept comes from economics, and Munger considered it one of the most useful filters in decision making.
Munger and Buffett applied it directly when choosing investments. Rather than asking whether an opportunity was good in isolation, they compared it with the best thing they already had available. If a new idea was not better than that, it was not worth doing, however attractive it looked on its own. This kept their standards high and their attention focused.
The limit is using opportunity cost as a reason to keep reopening every decision. Constantly comparing an existing commitment with imagined alternatives leads to restlessness and wasted effort, since switching has costs too. The framework is most powerful when you are deciding whether to take something on, not as a way to second-guess everything weekly.
Opportunity cost is the natural partner of the sunk cost fallacy. Sunk costs look backward at what is already spent. Opportunity cost looks forward at what each option could still deliver.
Example
A friend asks you to join a weekly volunteer committee, and it sounds worthwhile. Before agreeing, you compare it with the best other use of those Thursday evenings, which is the language course you have been meaning to start. Seeing the two side by side makes it clear which one you value more.
Try it this week
Before saying yes to any new commitment this week, name the specific thing it will push out of your schedule.
From 12 Mental Models (Charles T. Munger · 1995).
