An understanding of Ecnomics may help to understand the behaviour of individuals and firms in the economy. This helps to understand the behaviour of prices and quantity demanded or supplied.
The demand curve from right to left and supply curve from left to right. The curve may shift due to the many reasons, such as availablity of substitutes.
Economics - Demand & Supply
The change in the price of substitute goods, will cause consumers to switch to the other. This is a typical consumer behaviour.