From My Spiritual Diary-60: "Controlling the Mind"

How hard it is to control the mind! Well has it been compared to the maddened monkey. There was a monkey, restless by his own nature, as all monkeys are. As if that were not enough, some one made him drink freely of wine, so that he became still more restless. Then a scorpion stung him. When a man is stung by a scorpion, he jumps about for a whole day; so the poor monkey found his condition worse than ever. To complete his misery, a demon entered into him. What language can describe the uncontrollable restlessness of that monkey? The human mind is like that monkey, incessantly active by its own nature; then it becomes drunk with the wine of desire, thus increasing its turbulence. After desire takes possession comes the sting of the scorpion of jealousy at the success of others, and last of all the demon of pride enters the mind, making it think itself of all importance. How hard to control such a mind?

The first lesson, then, is to sit for some time and let the mind run on....Until you know what the mind is doing you cannot control it. Give it the rein; many hideous thoughts may come into it; you will be astonished that it was possible for you to think such thoughts. But you will find that each day the mind's vagaries are becoming less and less violent, that each day it is becoming calmer.....we must patiently practise every day.....It is a tremendous work, not to be done in a day. Only after a patient, continuous struggle for years can we succeed.

Excerpt from the Complete Works of Swami Vivekananda.