And many of these would have God will that which they themselves will, and are fretful at having to will that which He wills, and find it repugnant to accommodate their will to that of God...Thus they measure God by themselves and not themselves by God. 

- St. John of the Cross

St. John of the Cross teaches a hard lesson. In our prayer practice, we too easily believe that pleasure, relief, comfort, and agreeableness in prayer is the will of God. If we encounter the opposite feelings, we consider the prayer faulty and not according to God's will. Thus, we abandon the prayer, thinking that God only wills the pleasant, the relieving, the comfortable, and the agreeable. St. John teaches that this mistake leads one away from God, off the spiritual path, and, most directly, hampers our life of prayer from actual progress.