Why the value cannot be calculated? Let's look through the following instance: a bottle of water now has a price of $0,2 in Vietnam, but if I sell it at the price of $10, will you purchase it? I bet you will not buy it, right? However, let's imagine you are in a desert, you are about to die, if I sell this bottle of water at the price of $100, will you buy it? For me, I will purchase it. As you can see, the value of this bottle varies according to the context. Exactly, the value can vary according to times and context and it can be different for different people.