This paper shows that the moving or time-varying large components of four-component wavefunction of electron would induce small components, and vice versa. Then when a wave packet of electron is moving with high speeds or varies rapidly, or its size is sufficiently small, or in the presence of a strong electromagnetic field, its small components and the related effects cannot be ignored. Furthermore, the spin quantum states of both a moving electron and a motionless electron can be affected by some special electrostatic fields. This may open a new pathway for spintronics to the manipulation of electron spins in the absence of applied magnetic fields.