To one who has faith, no explanation is necessary. To one without faith, no explanation is possible. - Thomas Aquinas
Practice having faith when you play. Have faith that your hands will do exactly what you've asked of them. Trust your magnificent body. Excessive tension is a physical manifestation of fear brought about by doubt and worry. It keeps the body from acting in a natural way. Train your body well through practice, but let go of the need to control it. Relax and observe your hands with a continuous strong faith and you will be highly rewarded.