CFA2的Fix Income—— Yield curve movement and Forward rate部分有一段提到：

Thus, if a trader expects that the future spot rate will be                  lower than what is predicted by the prevailing forward rate, the forward contract                  value is expected to increase. To capitalize on this expectation, the trader would                  buy the forward contract.
理解不了为什么forward contract value会上升？求教，谢谢！