For general systems, the best we can hope for is that the expected position and momentum will approximately follow the classical trajectories. If the wave function is highly concentrated around a point x 0 , then V ′ ( ⟨ X ⟩ ) and ⟨ V ′ ( X ) ⟩ will be almost the same, since both will be approximately equal to V ′ ( x 0 ) . In that case, the expected position and expected momentum will remain very close to the classical trajectories, at least for as long as the wave function remains highly localized in position.