A million shellfish and one boy

Ms Krohn retold this story, it goes something like this:

There was a beach that, when the tide was out, had literally millions of shellfish exposed to the searing heat. One boy was there whenever the tide was out to throw the shellfish on the beach back into the sea.

A person saw what the boy was doing and asked him:"there are so many shellfish out here, what difference are you going to make? You'll never be able to save the lives of all these shellfish."

The boy picked up a shellfish and threw it back into the water and replied:"It made a difference to that one."