The mind is like a monkey

There was a monkey, restless by his own nature, as all monkeys are. As if that were not enough someone 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.

Swami Vivekananda, Raja-Yoga