Once Buddha was passing by a lake with few disciples, they stopped there for a while and Buddha asked one of his disciples I am thirsty can you please get some water from lake.
The disciple walked to lake, when he reached it he saw few people are washing clothes in the water and right at that moment bullock cart was crossing through the lake. As a result disciple thought how can he give this muddy water to drink. So he came back and told that water is dirty I think it is not fit to drink.
After half an hour passed Buddha asked same disciple to go to lake and get the water and disciple obediently went there.
This time the disciple found lake had clear water, the mud had settled down and the water was fit to drink so he filled the pot with water and went back.
Buddha Looked at water and than at disciple and said see what you did to make water clean you let it be. The mud settled down on its own and you got clear water. Our mind is also like that when it is disturbed just let it be, give it a little time it will settle down on its own. You do not have to put any effort to calm it down. It is effortless.
When you feel disturbed unable to focus or concentrate don’t worry just take deep breaths and calming thoughts will come. Let the peace flow around you.