Aerosols are postulated to alter moist convection by increasing cloud droplet number concentration (Nd). Cloud-resolving model simulations of radiative-convective equilibrium show that higher Nd leads to stronger convective mass flux, seemingly in line with a hypothesis that links the convective invigoration to delayed rain formation allowing more cloud liquid condensate to be frozen. Yet, the invigoration is also present in an alternative model configuration with warm-rain microphysics only, suggesting that ice microphysics is not central to the phenomenon. The key dynamical mechanism lies in the different vertical distributions of the increases in water vapor condensation and in cloud liquid re-evaporation, causing a dipole pattern favoring convection. This is further supported by a pair of mechanism-denial experiments in which an imposed weakening of cloud liquid re-evaporation tends to mute invigoration.