Why does the Yield of a Bond fluctuate?

The yield is the effective interest rate that one earns from bonds. It is a function of coupon and market price. As the market price of Bonds fluctuates due to varying macroeconomic and sector-specific/ issuer-specific factors, so the Bond Yields also change with time. However, it is to be kept in mind that once an investor has purchased a Bond at a certain price, the investor’s yield remains fixed till maturity of the Bond.