Opportunity cost

In economy there is an expression which I like a lot and it is ¨the cost of opportunity¨. Basically it is what we don´t get or what we renounce when we take a decision. Or put another way, the benefits you could have received by taking an alternative action.
You can apply this theory to economy, for example, if an asset such as capital is used for one purpose, the opportunity cost is the value of the next best purpose the asset could have been used for. And also you can apply it to real life. For example if one evening you decide to go to the cinema, the cost of opportunity would be the alternatives not chosen and lost (in a way) at that moment. It would be easier if we knew the outcome in advance but this is known only looking backwards.