Sorrow and happiness are the heresies of virtue; joy and anger lead astray from TAO; love and hate cause loss of virtue. The heart unconscious of sorrow and happiness - that is perfect virtue. One, without change - that is perfect repose. Without any obstruction - that is the perfection of the unconditioned. Holding no relations with the external world, - that is perfection of the negative state. Without blemish of any kind, - that is the perfection of purity.
ZhuangziIf you persist in trying to attain what is never attained (It is Tao's gift), if you persist in making effort to obtain what effort cannot get, if you persist in reasoning about what cannot be understood, you will be destroyed by the very thing you seek. To know when to stop, to know when you can get no further by your own action, this is the right beginning!
Zhuangzi