Many years ago, a farmer happened to see the King's daughter in the capital. He lost his heart to her at once. After returning, he missed the princess day and night. Soon, he was ill. His friends and relatives came to see him. When they knew the reason why the farmer was ill, they thought it was quite difficult to help the farmer, for the King would never consent to his daughter marrying a poor man. But the sick man sighed sadly: "If I can't get the princess, I will be dead." His friends tried to persuade him, but in vain. So they had to play a trick. Some days later, they came to see the man again and told him they had asked the princess to marry him, but she rejected. In fact, they had never done it. But the foolish man believed. However, he did not give up his mind. He announced: "if I visit the princess in person, she will say yes." If he did so, you can guess the result.

Later,people use it to describe the man who only considers his own aspiration, ignoring the objective situation and others' opinions.

从前，有个农夫偶然在国都看见了公主，顿时被她的美貌倾倒。回家后，天天思念，不久就生病了。他的亲人和朋友都来看他。他们知道农夫想娶公主后，觉得事情 很难办。因为国王是不会把女儿嫁给一个农夫的。可这个农夫叫道：“得不到公主我会死的。”朋友们说服不了他，只好想了一个办法骗他。几天后，他们又来看农 夫，并告诉他他们去见过公主，但公主拒绝了他们的请求。其实，他们根本没见过公主。但农夫相信了朋友们的话，可他并不死心。他认为如果他亲自去，公主一定 会答应。你可以猜想如果他亲自去会有什么结果。

后来，人们就用“一厢情愿”来比喻一个人只顾自己的想法，不管当时的客观情况，也不理会别人的看法。

一厢情愿 (yī xiāng qíng yuàn)
【翻译】Only One Side is Willing.
【释义】指单方面的愿望或不考虑客观实际情况的主观意愿。同“一相情愿”。
【例句】那个男生并不喜欢那个女生，她只是一厢情愿地跟着他。
【近义词】心甘情愿
【反义词】两情相悦