There is a direct relationship between supply and demand, as supply usually rises when demand is high. Initially there is what is known as excess demand when the currently available supply is unable to fully meet requirements. This leads to a rise in the market price, which in turn causes more companies to offer the relevant good because they can earn a lot of money by doing so (at least at that point in time).
As a consequence of this, the effect is frequently reversed, as the more expensive a product or service is, the less demand there is for it, as potential buyers look around for cheaper alternatives. This results in excess supply. The market price falls until the relevant good is sufficiently affordable that buyers’ interest – and thus demand – rises again.