And so to jerf&#x27;s point, somebody starving places high value on getting one orange, or two. But by the time he&#x27;s got a pile of a billion oranges, he&#x27;s really not interested in getting any more. Looking at it the other way around, if you give Bill Gates a check for $1,000, he won&#x27;t notice it. If you gave that same check to a homeless person, or to an impoverished would-be entrepreneur in India, it may change his life.<p><i>but [money] isn&#x27;t really what economics is about.</i><p>David Friedman, son of the famous Milton, wrote:<p><i>Economists are often accused of believing that everything  – health, happiness, life itself – can be measured in money.  What we actually believe is even odder.  We believe that everything can be measured in anything.</i><p>To answer the obvious follow-up:<p>Economics is the study of choices: what makes a person choose Option A rather than Option B. So the core concept in economic is <i>opportunity cost</i>.