The normal progression of a ballroom dancer (if there is such a thing as normal) is to learn footsteps, then elements, then patterns. Unfortunately, most dancers stop right there and fail to progress any further. I call these dancers "pattern dancers". "Pattern dancers" are basically two-legged dancers creating two-legged feelings. It is similar to two runners running beside each other with an arm on each other, each doing the same thing but separately. If you remain a pattern dancer, you will eventually become bored with your dancing. No matter how many patterns you learn, they all eventually become the same.
The next step in the progression is to develop four-legged movement that creates the unique four-legged feelings. Four-legged feelings cannot be created except through connection and partnership. A single unque feeling is developed when you move as one on the dance floor (one two-headed four-legged animal).
The four-legged dancer enjoys and feels each and every step of the four-legged movement. Pattern dancers have a tendency to dance a whole pattern and actually miss the four-legged feeling of each step. Our goal is to develop four-legged feelings because that is where all the good stuff resides.
The mentality of the "pattern dancer" is basically the same on both sides of the partnership. The "pattern dancers" are fundamentally just mirroring each other as they move. I describe it as "lead and follow". The leader does something and the follower responds.
The mentality of each side of the four-legged partnership is quite different. I like to describe it as "lead and add to the lead, enhance the lead, power the lead, participate in the lead". This means that the leader must also allow and participate in the followers' actions. The leader uses and encourages the participation of the follower. Both sides of the partnership participates and enhances every step, one step at a time.
The leader controls the power and movement of the two-headed four-legged animal in various ways. The partnership has an inward connection toward each other (center of the partnership) allowing each side of the partnership to feel and know where the other half is at all times. This is very important to maintain the continuous counter balancing and exchange of power of the partnership. The inward connection also allows the partnership to stretch within itself and create the four-legged feeling of a single entity (the two-headed four-legged animal). When the leader powers from the supporting leg, the follower feels the power and adds to the power from her supporting leg, but the movement is still under the control of the leader.
For example, when the leader initiates a movement, the lady adds to that movement. At this point, the lady doesn't know where she is going. As a trained dancer, she knows to continue moving until she feels the leader stop her movement. The leader senses the ladies power and adjusts his lead accordingly so the partnership ends up at the proper place. The leader actually stops his lead early and allows the ladies' power and momentum to finish the partnerships movement. This can only happen if the above mentioned connection is maintained. This is what true four-legged movement is all about and this is what creates the unique four-legged feelings.
Ultimately, there aren't two half's of the partnership, just a single entity, the two-headed four-legged animal moving as its own entity creating the unmistakable four-legged feelings.