A shift in demand curve: a shift in demand curve occurs when there is a change in the factors affecting demand, price (of the good) being constant. Factors affecting the demand are consumers' income, preferences of the consumers, price of substitute goods, and others. Demand curve shifts in two directions that are, right and left. For example, if demand increases due to an increase in consumers' income, then demand curve will shift to the right, and when demand decreases due to a decrease in the income of consumers, then demand curve will shift to the left.

Shift in the supply curve: a shift in supply curve occurs when there is a change in the factors affecting supply, price (of the good) being constant. Factors affecting the supply curve are changes in technology, change in government policies, change in production cost, and others. Supply curve shifts in two directions which are, right and left. For example, if the production cost rises, then supply will fall, and the curve will shift to the left, but if the cost of production decreases, supply will increase, and the curve will shift to the right.