This study proposes a theoretical model based on quantum mechanics—specifically deriving a Schrödinger equation to model stock return dynamics—to explain investor behavior. By analyzing S&P 500 data from 1992 to 2021, the authors demonstrate that “herding” (investors mimicking each other) is counter-cyclical: it is significantly stronger during recessions than during economic booms. The research identifies economic uncertainty as the critical mechanism; as uncertainty rises during downturns, information asymmetry forces investors to abandon independent valuation in favor of following the crowd, a behavioral shift that the quantum model successfully predicts via power law exponents in return distributions.