Why do increases and decreases in quantity of demand not shift the position of the demand curve?

Increases and decreases in quantity demanded are movements along the demand curve, not shifts of the curve itself. These changes occur in response to price fluctuations, reflecting the law of demand, which states that as price decreases, quantity demanded increases, and vice versa. In contrast, shifts of the demand curve result from changes in non-price factors such as consumer preferences, income, or the prices of related goods, which alter demand at every price level. Thus, while quantity demanded changes with price, the underlying demand curve remains in place unless these other factors change.