Horse bits are used to control a horse.
This is a true statement. However, to be used correctly the bit must be combined with other aids to be effective. The other aids being, the legs, trunk , body weight, and the head. The head aid is important because thought even for a split second it must precede any physical action taken. When thought produces physical action and it is made thoughtlessly it may also be irrational. Body weight and the hands act as an aid through the bit, which supports and follows the aids given by the legs, seat and trunk. The hand should always be the last aid in the chain of applying the riding aids.
If a rider is ineffectual when applying the leg, or if the upper body is insufficiently balanced, soft and supple so as to conform to the movement of the horse. Then the entire system will not be effective in achieving the desired results of the any bit being used.