As more cookies are eaten, consumers are willing to pay less for each additional cookie because it gives them less satisfaction than the previous cookie. When price is high, quantity demanded is low. When price is low, quantity demanded is high. This inverse relationship is the Law of Demand. Price is the most important reason cookie buyers, or any buyers in any market for that matter, do what they do.
Price also controls suppliers' willingness and ability to bring products to the marketplace.
Price must cover suppliers' costs for land, labor, capital and other costs incurred in providing the product or service. Capital, as used by economists, means equipment and machinery. At a higher price, suppliers will be more willing and able to bring more products to sell because they will make more money. When prices are low, suppliers are less willing and able to offer products. So the Law of Supply is a direct relationship between price and quantity supplied.