• "I like this coat but I can't buy it because it's too expensive. I will settle for something cheaper."
• "You can't fill your car's tank with 50 euros!"
• "You can't build a car out of wood."

Every day we have to make choices between what we want to buy and what we can afford to buy, and we understand that the money we can spend is not enough to buy what we want. Just think about the additional things we could buy if our income was higher - new clothes, new furniture, a better car, a blue ray DVD, a new mobile phone.

The list is endless, because even if we instantly acquire what we want, new things (goods) that we will want to buy will soon come up. Also, in the example of building a car out of wood, we understand that in order to create a good, the appropriate materials must exist and be combined in a specific way.