When you lunge your horse mindlessly, not caring about manners, attention or learning, all you will get is a fit horse without manners. To foster the proper relationship between you and your horse, with you as the one who leads and plans and your horse as the one that does the physical work. To develop your horse's forward urge. In short, when you lunge, you should not just run your horse around in a circle. Instead, imagine sending the horse forward, in response to your body energy.
Trainers usually advocate using a whip to send the horse forward on the lungeline.
If this has been your style, we don't require you to stop it, but merely ask you to give up the whip for a few weeks so that you can explore and develop your personal energy, which the use of the whip tends to inhibit. To start out, replace your whip by learning to spin a lunge rope. Drop the whip, at least temporarily, for a second very important reason. In lunging, the two hands have two different functions. However, at least equally important is the hand that holds the lungeline, which is called the directing hand.