"When the great library of Alexandria was burned, one book was saved. But it was not a valuable book; and so a poor man, who could read a little, brought it for a few coppers. It was not very interesting; yet there was a most interesting thing in it! It was a thin strip of vellum on which was written the secret of the "Touchstone."
The touchstone was a small pebble that could turn any common metal into pure gold. The writing explained that it was on the shores of the Black Sea, lying among thousands and thousands of other pebbles which looked exactly like it. But the secret was this. The real stone would feel warm, while ordinary pebbles are cold. So the man sold his few belongings, brought some simple supplies, camped on the seashore, and began testing pebbles. This was his plan.
He knew that if he picked up ordinary pebbles and threw them down again because they were cold, he might pick up the same pebble hundreds of times. So, when he felt one that was cold, he threw it into the sea. He spent a whole day doing this and there were none of them the touchstone. Then he spent a week, a month, a year, three years; but he did not find the touchstone. Yet he went on and on this way. Pick up a pebble. It's cold. Throw it into the sea. And so on and on.
But one morning he picked up a pebble and it was warm...He threw it into the sea. He had formed the 'habit' of throwing them into the sea. He had gotten so into the habit of throwing them into the sea, that when the one he wanted came along...He still threw it away." From, "Your Greatest Power"