In this short article, the author demonstrates that real interest rates cannot be lower than -1 (i.e. -100%). He discusses how the textbook approximation to the Fisher equation can lead to the erroneous belief that there is no lower bound on real interest rates. He also speculates that the widespread use of the Fisher equation is why we had yet to realize that a lower bound on real rates exists. This leads him to advocate using and teaching the exact Fisher equation, rather than its approximation.