We apply an option-based measure of firm-level discount rate and discount rate revision to the factor zoo. A simple test separates factors into two groups: those that reflect rational risk compensation and mispricing. Mispricing factors are on average more significant statistically and economically than rational factors. Notable mispricing factor categories include volatility, profitability, external financing, short-sale constraints, and momentum. Mispricing factors’ long-short unexpected returns exhibit strong time-series comovement. So do their long-short discount rate revisions. Controlling for discount rate revisions renders the mispricing factor zoo statistically insignificant. Discount rate (cash flow) revision explains a larger fraction of time-series (cross-sectional) variation of the mispricing factor zoo.