图源网络

During the Spring and Autumn Period (770-476 BC), 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. 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.

Sun Yang wrote 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 thought it was very easy to appraise horses according to the book. So he took it with him to look for fine horses. He found the characteristics of a toad fit very well the characteristics described in the book. So he happily took the toad back home, Sun Yang did not know whether he should laugh or cry. "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. Sometimes it is also used to refer to trying to locate something by following up a clue.

中国成语故事：按图索骥

春秋时，秦国有个名叫孙阳的人，善于鉴别马的好坏，他把自己识马的经验写成书，名为《相马经》。这本书图文并茂地介绍了各类好马，所以人们把孙阳叫“伯乐”。

书上写着：良马有高高的额头，鼓起的眼睛，马蹄是圆圆的。孙阳的儿子熟读了这本书后，以为自己学到了父亲的本领，便拿着《相马经》去找好马。一天，他在路边看见一只癞蛤蟆，前额和《相马经》上好马的特征相符，就以为找到了一匹千里马，马上跑去告诉父亲：“和你书上画的好马差不多，只是蹄子不像。”孙阳听后，哭笑不得，开玩笑地说：“这匹马太喜欢跳了，不好驾驭。” 这个成语比喻机械地照书本上的知识，不求事物的本质。