Venus' modern retrograde rotation is most likely the product of atmospheric braking combined with a slow initial rate of rotation.

However, slow rotation and even outright tidal locking does not necessarily rule out long-term habitability. Oceans and atmospheres can transfer absorbed energy, for instance. In "Strong Dependence of the Inner Edge of the Habitable Zone on Planetary Rotation Rate", Yang et al. argued that a slower rotation rate is beneficial the closer a planet is relative to its host star.