Parapharese this text. A demand curve shows how the quantity demanded changes in response to a change in price, if all else remains constant. But things may change and demands may change, this causes the demand curve to shift to suit demands of alternatives. This information is important because it allows us to track the demands were filling and set prices adequately to get efficient results. The whole ideology of meeting supply and demand is to be in the equilibrium of price. Which is when the quantity of a goods demanded in a time equals the quantity supplied. So, when MarketDemand and Market Supply cross, its where Equilibrium price can be ascertained. Whenever the market is set above or below the equilibrium price, either a market surplus or a market shortage is eminent