Ki is spiritual energy that comes from not the mind, but the heart. Ki is used by Psychics more often than anybody else. even though Ki is very useful, but it is used seldom considering it drains the life of the user and decreases their power. Sometimes, if they attain the highest technique they can learn, they can choose three techniques of which will not drain their powers. There are over 75 Techniques with Ki. They call these techniques Kichan or Spiritual techniques.
It is compared to trying to destroy a piece of paper. It can be hard, or extremely easy.