In the short run , expected future spot rates determine the shape of the yield curve . In the long run , it is less likely that investors have confidence in 1-year spot rates several years from now ( e.g.,30 years ). Thus , expectations are unable to describe the shape of the term structure for long - term horizons . However , it is reasonable to assume that real rates and inflation rates are relatively constant over the long run . For example , a short - term rate of 5% may imply a long - run real rate of interest of 3% and a long - run inflation rate of 2%. Thus interest rate expectations can describe the level of interest rates for long - term horizons . 请问，这两段话怎么理解呢？第一段说预期无法描述长期期限结构的形状。第二段又说利率预期可以描述长期利率水平。利率预期都能描述长期利率水平了，为什么不能描述长期期限结构的形状呢？
