Walking on the sand beach as usual, the boy found a weird looking creature.
People don't notice it because they are tired and in a hurry.
He thought that it was lost, so he tried to find where it belongs.
However, everybody including strangers, his parents and his friend who has a lot of knowledge did not know about it and rejected it.
At last, he found the world where such creatures live and said goodbye to it.
The lost thing represents the discovery in the childhood.
I think the author is criticizing the indifference of adults.
