MONKEY

Buddhism refers to the “monkey mind,” but Vedanta uses the metaphor, too.

Swami Vivekananda compared the human mind to a monkey that is always restless and incessantly active by its own nature.  The human mind, he said, naturally wants to get outside, to peer out of the body, as it were, through the channels of the organs.
  
Accordingly, he stressed the practice of concentration, as he felt there is no limit to the power of the human mind; the more concentrated it is, the more powerful it becomes.  It Is important, he said, to avoid anything that disturbs the mind or makes it restless.

In his lectures on Raja Yoga, he suggested that a person "Take up one idea.  Make that one idea your life; think of it, dream of it, live on that idea.  Let the brain, muscles, nerves, every part of your body, be full of that idea, and just leave every other idea alone.”  In religion, coincidentally, this was the way great spiritual giants were produced, he said.