When an investor believes future spot rates will be below the forward rates implied by the current yield curve, they should buy a forward contract. This is because:

• Forward rates represent the market's expectation of future spot rates
• If actual future spot rates turn out to be lower than forward rates, the investor benefits from locking in the higher forward rate
• Buying a forward contract allows the investor to profit from this discrepancy

For example, if the 1-year forward rate is 5% but the investor believes the actual 1-year spot rate will be 4%, they can lock in the 5% rate by buying a forward contract.