This is a funny idiom about the most famous horse expert in China...Bo Le. He was a resident from the country of Qin. He recorded everything he knew about horses in an anthology of books called "Shiang Ma Jing." Which was like an encyclopedia on thorough bred horses. His writings could be used to find the fastest, strongest horse...mostly for military/sporting purposes.
Bo Le had a little son who was obsessed with finding the finest horse on his own. The little boy had thoroughly read the "Shiang Ma Jing" over and over, inside and out. One day he went off to look for a horse on his own. Shortly after running outside, he was SO sure he found a horse that matched the description in his father's books. The boy threw the horse into a sack and excitedly ran to show it off to his father.
Bo Le's son took the horse out of the sack and waited for his father's validation. Turns out, the horse in the sack...was a huge toad! Bo Le laughed and joked to his son: "This horse of yours sure likes to jump, but I don't think anyone can ride it!"
Moral of this idiom: don't always stick by the book (or the rules) also, get your information from multiple sources before coming to a conclusion
ORIGINAL IDIOM: 按图索骥
伯乐是春秋时最会相马的人，他总结自己多年相马的经验，写成一本书，叫 “相马经。” 他的儿子把 “相马经” 背得滚瓜烂熟，准备 “按图索骥” 照书上的标准，去寻找千里马。
几天后，他儿子高高兴兴地回来了，对伯乐说：我找到千里马了！这马和 “相马经” 讲的差不多，就是蹄子不大像。说完，他从布袋里倒出一只大癞蛤蟆来。