①When the great library of Alexandria burned, the story goes, and one book was saved. But it was not a valuable book, and a poor man got it.
②The book wasn't very interesting, but between its pages there was something very interesting indeed. It was a thin strip of vellum(羊皮纸) on which was written the secret of the " Touchstone. The touchstone was a small pebble( 鹅卵石) that could turn any common metal into pure gold.
③The writing explained that it was lying among thousands and thousands of other pebbles that looked exactly like it. But the secret was this: The real stone would feel warm, while ordinary pebbles are cold.
④So the man sold his house, bought a tent, camped on the seashore and began testing pebbles. He knew that if he picked up normal pebbles and threw them down again because they were cold, he might pick up the same pebbles hundreds of times. So, when he felt one that was cold, he threw it into the sea. He spent a whole day doing this but none of them was the touchstone. Yet he went on and on this way. Pick up a pebble. Cold - throw it into sea. Pick up another. Throw it into the sea. The days stretched into months and the months into years.
⑤ One day, however, about mid- afternoon, he picked up a pebble and it was warm. He threw it into the sea before he realized what he had done. He was used to throwing each pebble into the sea as soon as he picked it up. So when the one he wanted came along, he still threw it away.
⑥ Opportunity knocks but once. Unless we are vigilant(警惕的), it's easy to fail to realize an opportunity when it is in hand and it's just as easy to throw it away.
(①=Para. (自然段)1 ②=Para. 2 ③=Para. 3 ……)
