If the mind is always calm and still, dark and silent, not seeing anything, neither inside nor outside, free of all thoughts and mental images, this is the settled mind, which is not to be conquered.  If the mind gets excited at objects, falling all over itself, looking for beginnings and ends, this is the confused mind, which ruins the virtues of the Way and undermines essence and life – it should not be indulged.  Putting your nature in order is like tuning a stringed instrument.  If the strings are too taut, they will snap.  If they are too loose, they will be unresponsive.  When tautness and relaxation are balanced, then the instrument is ready.

Wang Chongyang