Leader of the movement
A leader is someone or something that others follow. If a number of people have to go through a tunnel that is only large enough to fit a person through at a time, the first person who goes through it is the leader, whom the rest of the people just follow. If multiple people try to go through the tunnel at the same time, there will be a jam, and no one can come out the other end.
Let's apply this idea to the three-count positive circle. In the first count (in-with-elbow), the elbow is the leader, and everything else gives way. In the 2nd count (turn-with-waist), the waist (we will use the term kua at a higher level) is the leader. In the 3rd count (out-with-hand), the hand (middle finger later on) is the leader. There should never be the case that during in-with-elbow, the hand competes with the elbow and tries to lead. Similarly, during out-with-hand, the elbow should not compete with the hand.
There are cases where elbow is the leader at the beginning, the elbow stops and the hand takes over as the leader. At no time, there are two leaders.
The leader does not imply the location of power though there may be occasions that the leader happens to be the location of power. Where power is generated can change as required by the situation. Our power will be at a place where the opponent's power is not.
Out-with-hand is like threading through a needle, while in-with-elbow is like pulling a thread out of a needle. The elbow causes the hand, which is the tip of the thread, to move on a track while the hand itself does not move.
Also note that once we have threaded through a needle by a little bit, we would switch to hold the tip of the thread that has passed through the hole and pull in order to get more thread through easily. The hole of the needle itself is a demarcation. The switching of the place that the hand is holding is related to the concept of "Dao Shou". If somehow we are able to get to the other side, we will simply pull with respect to the demarcation. This is the idea of "making every push a pull".
When this concept is understood and the body achieves this ability to have "leaders", we say one has the ability to lingjin (领劲 - to lead the energy).