The unemployment rate is one example: https://fred.stlouisfed.org/series/UNRATE https://fred.stlouisfed.org/series/UNRATE As I understand it, the theory basica

The unemployment rate is one example: https://fred.stlouisfed.org/series/UNRATE https://fred.stlouisfed.org/series/UNRATE As I understand it, the theory basically goes like this: Low unemployment leads to higher labor costs, which leads to wealthier workers and higher demand for products, which leads to even higher demand for labor. Essentially a positive feedback loop of inflation, which the Fed will stop by increasing interest rates. They may notice too late, or be late deliberately, and thus have to raise interest rates a lot and fast.