The bridle is a tool which sets boundaries telling a horse where not to go.  It is used for blocking unwanted direction.  The right rein should not be pulled to steer the horse to the right.  This will throw the horse off balance.  Instead it blocks the horse from going to the left.  The left rein does not pull to steer the horse to the left.  It simply blocks the horse from going right.  Pulling creates stress in the horse and does not elicit a sense of trust.  Is your horse in good hands?