Once Buddha was travelling with a few of his followers. While they were passing a lake, Buddha told one of his disciples, "I am thirsty. Do get me some water from the lake."
The disciple walked up to the lake. At that moment, a bullock cart started crossing through the lake. As a result, the water became very muddy and turbid. The disciple thought, "How can I give this muddy water to Buddha to drink?"
So he came back and told Buddha, "The water in there is very muddy. I don't think it is fit to drink."
After about half an hour, again Buddha asked the same disciple to go back to the lake.
The disciple went back, and found that the water was still muddy. He returned and informed Buddha about the same.
After sometime, again Buddha asked the same disciple to go back.
This time, the disciple found the mud had settled down, and the water was clean and clear. So he collected some water in a pot and brought it to 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 let it be, and the mud settled down on its own -- and you have clear water.
Your mind is like that too! When it is disturbed, 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.