Economic logic is based on the notion of scarcity, according to which needs outstrip resources.
By resources we mean staff, time, buildings, capital, goodwill, equipment, power and all else that we need to use to meet a need. In order to trade resources and services, money is used. As resources are scarce it is necessary to make choices not just on which needs should be met and which should not but also on assessing up to which point several different needs should be met. However, as resources are scarce each decision to use resources implies a sacrifice. This is because once resources are used in a certain way, they cannot be used in an alternative manner.