A thirsty Crow came upon a Pitcher which had once been full of water; but when the Crow put its beak into the mouth of the Pitcher he found that it was only half full, and that he could not reach far enough down to get at the remaining water. He tried, and he tried, but at last had to give up in despair. Then a thought came to him, and he took a pebble and dropped it into the Pitcher.  
 
Then he took another pebble and dropped it into the Pitcher.  
and then another pebble and dropped that into the Pitcher.

At last, after many pebbles, he saw the water mount up near him, and after casting in a few more pebbles he was able to quench his thirst.
 
Little by little does the trick.