Standard demand elasticity estimation treats investors’ demand slopes as stable objects that can be traced out by exogenous residual supply shifts. We show this identification strategy fails in dynamic settings: supply shocks cause demand curves to tilt and shift through general equilibrium effects. The mechanism is intuitive — investors’ demand depends on the entire distribution of current and future returns, including volatility, covariances, and correlations with investment opportunities. Supply shocks that change today’s prices inevitably reshape future return distributions, moving the demand curve itself. We develop and calibrate a dynamic model to quantify this mismeasurement. The measured slope is approximately 40% of its conceptual counterpart, implying that demand curves are substantially steeper than estimated. This distortion operates through two channels: endogenous risk (altered volatility and covariances) and amplified intertemporal hedging (changed correlation with investment opportunities). The distortion remains sizable even for infinitesimal or purely transitory shocks.