Shift back and forth is a term used to describe an action of wavering or fluctuating. It is often used to describe a person's behavior or attitude that changes rapidly and unpredictably. WAVER is defined as to move or sway unsteadily from side to side, while FLUCTUATE is defined as to change continually in amount, degree, or intensity. Therefore, shift back and forth is an apt description for an action that is characterized by rapid and unpredictable changes.