按圖索驥

春秋時候，秦國有個叫孫陽的人，擅長相馬，無論什麼樣的馬，他一眼就能分出優劣。他常常被人請去識馬、選馬，人們都稱他為伯樂（「伯樂」本是天上的星名，據說負責管理天馬）。

有一次，孫陽路過一個地方，忽見一匹拖著鹽車的老馬衝他叫個不停，走近一看，原來是匹千里馬，只是年齡稍大了點。老馬拉著車艱難地走著，孫陽覺得太委屈了這匹千里馬，它本是可以奔跑於疆場，可以發揮更大作用的寶馬良駒，現在卻默默無聞地拖著鹽車，慢慢地消耗著它的銳氣和體力，實在可惜！孫陽想到這裡，難過得落下淚來。

為了讓更多的人學會相馬，使千里馬不再被埋沒，也為了自己一身絕技不至於失傳，孫陽把自己多年積累的相馬經驗和知識寫成了一本書，配上各種馬的形態圖，書名叫《相馬經》。

孫陽有個兒子，看了父親寫的《相馬經》，以為相馬很容易，就拿著這本書到處找好馬。他按照書上所繪的圖形去找，一無所獲。又按書中所寫的特徵去找，最後發現有一隻癩蛤蟆很像書中寫的千里馬的特徵，便高興地把癩蛤蟆帶回家，對父親說：「爸爸，我找到一匹千里馬，只是蹄子稍差些。」父親一看，哭笑不得，沒想到兒子竟如此愚笨，便幽默地說：「可惜這馬太喜歡跳了，不能用來拉車。」接著感歎道：「所謂按圖索驥也。」

故事出自明朝楊慎的《藝林伐山》。成語「按圖索驥」，比喻機械地照老辦法辦事，不知變通；也比喻按照某種線索去尋找事物。

Looking for a Steed with the Aid Of Its Picture

During the Spring and Autumn Period, there was a man in the State of Qin whose name was Sun Yang. Sun Yang was very expert in looking at horses and judging their worth. Whatever the horse might be, he could tell whether it was good or bad at first sight. People called him Bo Le (Bo Le was the name of one of the celestial bodies and was fabled to be in charge of heavenly steeds), and he was often asked to appraise and select horses.

One day, when Sun Yang was passing a place, an old horse pulling acart loaded with salt suddenly neighed to him without stopping. He came near, and saw that it was a horse that really could cover a thousand Li a day, and that the only problem with it was that it was a little too old. The old horse was pulling the heavy cart with difficulties and hardships. Sun Yang felt acutely that the horse was really unjustly treated, for it might have been a fine steed galloping on the battlefield. It was a great pity that it was pulling the cart loaded with salt without attracting public attention, which had taken the edge off its spirit and consumed its energy. When he thought of this, he was so grieved that he shed tears.

In order to help more people learn how to appraise horses so that fine horses which could cover a thousand LI a day would no longer fall into oblivion, and also in order to ensure that his unique skill in judging horses would not be lost, Sun Yang worte a book entitled The Art of Looking at Horses and Judging Their Worth, based on his experiences and knowledge accumulated over the years. The book was also illustrated with the pictures of various horses.

Sun Yang had a son who, after reading his father's The Art of Looking at Horses and Judging Their Worth, thought it was very esay to appraise horses. So he took the book with him to look for fine horses everywhere. At first he searched according to the pictures in the book, and accomplished nothing. Then he searched according to the characteristics of a toad fit very well the characteristics described in the book. So he happily took the toad back home, and said to his father, "Father, I have found a horse that can cover a thousand Li a day, only its hoofs are not good enough." Looking at the toad, Sun Yang did not know whether he should laugh or cry. Knowing that his son was stupid, Sun Yang said humourously. "It's a pity that this horse is too fond of jumping to pull a cart." Then he sighed, "That is just what we call looking for a steed with the aid of its picture."

Later, people have used the set phrase "look for a steed with the aid of its picture" to refer to handling affairs mechanically in the outmoded ways without being flexible. Somethimes it is also used to refer to trying to locate something by following up a clue. This set phrase originates in Lumbering in the Forest of Art written by Yang Shen in the Ming Dynasty （1368-1644）.