When the great library of Alexandria burned, the story goes, one book was saved. It was not a valuable book, so a poor man, who could read a little, bought it for a few coppers.
The book itself wasn't very interesting, but between its pages lay a thin strip of vellum. On it was written the secret of the "Touchstone"! The touchstone was described as a small pebble that could turn any common metal into pure gold. The writing explained that it lay among thousands of identical-looking pebbles on a beach, with one key difference: the real stone would feel warm to the touch, while ordinary pebbles are cold.
Driven by this secret, the man sold his few belongings, bought supplies, camped on the seashore, and began testing pebbles. To avoid testing the same cold pebble repeatedly, he developed a method: whenever he picked up a cold pebble, he threw it into the sea. He spent days, then weeks, then months in this relentless routine: pick up a pebble, feel that it's cold, throw it into the sea.
One midafternoon, he picked up a pebble, and it felt warm. Acting purely out of ingrained habit, he threw it into the sea before he realized what he had done. He had trained himself so thoroughly to discard every pebble that he discarded the very one he sought.
The story concludes with a lesson: So it is with opportunity. Unless we are vigilant, it is easy to fail to recognize an opportunity when it is in hand, and just as easy to throw it away.