First of all, it should be noted that the term “Doctor” in this idiom is not the one we are familiar with in modern society, but rather an ancient academic title that refers to a person of profound knowledge.
In ancient times, there was a learned scholar who was proficient in reading the Four Books and Five Classics, and had to chew the words carefully in everything he did. He believed that his knowledge was quite high, and no one in the world could compare to him.
One day, he went to the market to buy a donkey. After paying, he wanted the donkey seller to write a contract for him, but the donkey seller couldn't read, so he asked the learned scholar to write it for him. The man felt that this was an opportunity to show off his talent, so he gladly started writing and soon finished writing three sheets of paper full of content.
He read the contract he wrote with full confidence, feeling that it would definitely shock everyone. However, everyone was confused after listening, and there was not a single word related to “donkey” in the thousands of words written. The donkey seller sneered and said, “You just need to write down: I sold a donkey to you and received how much money from you on the date of a certain year, month, and day, isn't that enough?” The onlookers also began to mock the scholar. The scholar felt bored and walked away dejectedly with his donkey.
Perhaps a scholar has read extensively and is very talented, but when speaking or doing things, they must be concise and to the point, hitting the key points directly, and not full of nonsense, wasting others' time.
The idiom “A learned scholar buys a donkey” generally metaphorically refers to writing a piece of nonsense without getting the point. This idiom serves as a warning to people that one should be down-to-earth and not to seek attention by sensationalism, and one should pay attention to efficiency and focus on key points when doing things.
首先需要说明的是，成语中的博士并非现代社会我们所熟知的博士，而是古代的一种学官名，代指的就是学问渊博类型的人。
在古时候有个博士熟读四书五经，做任何事情都要咬文嚼字一番，自觉学问颇高，天下无人能比。
有一天他到集市上去买驴，付钱之后，就想让卖驴的人给他写个契约，可是卖驴人不识字，就请博士代写。博士觉得这是一个炫耀自己才华的机会，便欣然写起来，不一会儿便写完了满满三张纸。
他自信满满念完自己写的契约，觉得肯定能够震惊众人。然而大家听完都一头雾水，下笔千言竟没有一个字与“驴”有关。卖驴人轻蔑地说，你只需要写上某年某月某日我卖了一头驴给你，收了你多少钱不就完了吗？围观的众人也开始嘲笑博士，博士自觉没趣，牵着驴就灰溜溜地走了。
或许博士饱读诗书，很有才华，但是讲话做事，一定要简明扼要，直击重点，不要满篇废话，浪费别人的时间。
博士买驴这个成语一般比喻写文章废话连篇，不得要领。通过这个成语告诫人们，做人要实实在在，不要哗众取宠；做事要讲究效率，抓住重点。
