In August 2015, Janet Yellen, chair of the Board of Governors of the Federal Reserve System (the Fed), was feeling uncertain. Many were trying to anticipate her decision about whether she and the Federal Open Market Committee (FOMC) would raise interest rates at the upcoming September meeting. But Yellen herself wasn't sure. Yellen wanted to understand the perspective of those who continued to worry about the consequences of expansionary monetary policy. To do so, and to understand the policy tradeoffs she faced, she had to consider the history of events that led to her current conundrum.