A beef carcass might have 500 pounds of meat on it, but only 5-10lbs of that is tenderloin. If we all have enough money to buy tenderloin it doesn't immediately follow that cows are then made up of nothing but tenderloin. So the price of tenderloin will go up until the demand balances the supply again. You can take this and apply it nearly anywhere in the economy and find it'll be approximately correct for a great many situations.