It was Alfred Marshall who developed the Principles of Economics. In this principle, Marshall explained the relationship between supply and demand, along with the production costs and price. To better understand his concept, Marshall formulated a curve that is still being used nowadays to easily illustrate the certain point at which the market achieves equilibrium. When a company increases its supply of certain sneakers, it only tells us that they are probably on sale. This means that prices decrease while the demand for such sneakers increase. On the other hand, the price increases if the quantity of sneakers decreases; thus, the demand decreases as well.