This is one of the topics covered in Emei Qigong Level 1 workshop.  One common question frequently asked by students and qigong practitioners, "Why can't we use mind-intention to direct our flow of energy in our qigong practices and in healing others?".  An example of such practice is using mind-intention to direct our flow of energy to "exchange" energy with the tree.  These are very common qigong practices.  More often than not, you will find that most Qi-(Energy) cultivating practices or Qi-(Energy) healing techniques requires you to use your mind-intention to direct your flow of energy.  This technique of using our mind-intention to direct energy flow is highly effective and powerful.  It is ok to do this occassionally for a short time, however, prolonged usage over extended period of time creates health problems to the practitioners.

To understand this, one needs to first grasp the idea of the two systems in our Body Life Energy Field.  One is an Open System and the other is a Closed System. The functions of the Open System are firstly, to control the natural energy exchange between the universe and the human body and secondly, to release negative energy from the human body. The functions of the Closed System are firstly, to first prevent the positive energy in the body from leaking out and secondly, to block off and solidify the body to make it more resistant to intrusions from the negative energy outside of the body. Of these two systems, the Open system leads and guides the Closed system. In healthy people, the two systems are usually balanced. This kind of balance is what Qigong terminology calls "normal."

One of the fundamental goals of practicing Qigong is to strengthen and enhance this normality. When you practice with the correct gestures, breathing, vocalizations, mind intentions, and so on, the human body's Open and Closed systems are advancing to different states. The two systems progress from "normal" to "beyond normal" over a long-term Qigong practice. People use solid and strong to describe this state of being beyond normal.

The two systems are out-of-balance: 

(1) when the Open System opens too much, the Closed System will become weaker.  Then, the human body and universal energy will not be able to exchange well. Too much universal energy entering the body is similar to someone eating too much and not being able to digest properly. This hurts the body. If the Closed System weakens, the body loses a great amount of pre-birth energy and it is very easy for external negative energy to intrude. When there is less positive energy than negative energy, all kinds of maladies will occur.

Although the amount of internal negative energy that is dispersed will also increase, but the rate of dispersion can never catch up with the speed and scale at which the internal pre-birth energy is lost and the external negative energy enters.

(2) when the Open System is not open enough, the closed system will become too strong. The human and the universal energy are not in a normal, natural exchange. Too little universal energy entering into the body has the same effects as starvation, malnourishment, and loss of health.

If the closed system is excessively closed, it can preserve internal positive energy by preventing it from leaking too much and make it difficult for the external negative energy to intrude. But the excessively closed system is only preserving the existing pre-birth energy, and the small amount of positive external energy that enters is too little. This is the same as a person who only knows how to be frugal, but does know how to be industrious—assets and fortune are very easily used up without being replenished. Because the Open System is not open enough, the ability to disperse internal negative energy is weak. The internal negative energy that the body produces cannot be dispersed effectively, thus causing all kinds of physical maladies.

Now that we understand the functions of the two systems of our Body Life Energy Field, and the importance of their balance in relation to each other, then it is easy to see how the downsides of using mind-intention in Qigong practices come about.

When we use mind-intention to direct our energy to flow out and absorb in, we are forcing the Open System to stay open.  So, proloned period of doing this will bring about health problems arising from the Open System staying open too much, as in (1).