Once the Buddha was walking from one town to another with a few of his disciples. While they were traveling, they happened to pass a lake.
They stopped there and the Buddha told one of his disciples, "I am thirsty. Do get me some water from that lake."
The young disciple walked up to the lake. When he reached it, he noticed that right at that moment, a bullock cart had started crossing the lake. As a result, the water had become very muddy, very turbid.
The disciple thought, "How can I give this muddy water to the Buddha to drink!?"
So he went back and told the Buddha, "The water in there is very muddy. I don't think it is fit to drink!"
After about half an hour, the Buddha again asked the same disciple to go back to the lake and get him some water to drink. The disciple obediently went back to the lake.
This time too he found that the lake was muddy. He returned and informed the Buddha about the same. Once again, a few minutes later the Buddha asked the same disciple to go back to the lake.
The disciple reached the shore only to find that the lake absolutely clean with crystal clear water in it. The mud had settled down and the water above it looked pure enough to drink. So he collected some water in a pot and brought it to the Buddha.
Buddha looked at the water, and then he looked up at the disciple and said,"See what you did to make the water clean. You just let it be and the mud settled down on its own, and you got clear water!"
And then he addressed his disciples:" Your mind is just like that lake ! When it is disturbed, it gets all muddy and confused. So just let it be. Give it a little time. It will settle down on its own. You don't have to put in any effort to calm it down. It will happen. It is effortless.