闭门造车 Build a car behind closed doors
Explanation
比喻脱离实际，只凭主观办事。
It is a metaphor for being detached from reality and acting only according to subjective viewpoints.
Origin Story
话说古代，有个工匠要造一辆新车。他自认为技艺高超，于是关起门来，独自一人埋头苦干。他没去参考其他车子的设计，也没去观察人们的出行习惯，只是凭着自己的想法设计和制作。经过长时间的努力，他终于造好了一辆车。兴冲冲地推着车子出门，却发现这车根本无法行驶，车轮和路面根本不匹配。原来，他闭门造车，完全脱离了实际情况。
Once upon a time, there was a craftsman who wanted to build a new car. He considered himself a master craftsman, so he closed his doors and worked alone diligently. He didn't refer to other car designs or observe people's travel habits, but only designed and manufactured according to his own ideas. After a long time of effort, he finally built a car. He excitedly pushed the car out, but found that the car could not drive at all, the wheels and the road were simply not compatible. It turned out that he had built a car behind closed doors, completely out of touch with reality.
Usage
通常用于批评那些脱离实际，只凭主观臆断办事的人。
It is usually used to criticize people who are detached from reality and act only according to subjective assumptions.
Examples
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他闭门造车，设计的产品根本不符合市场需求。
tā bì mén zào chē, shèjì de chǎnpǐn gēnběn bù fúhé shìchǎng xūqiú。
He built a car behind closed doors, and the product simply does not meet market demand.
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不要闭门造车，要多听听大家的意见。
bùyào bì mén zào chē, yào duō tīng tīng dàjiā de yìjian。
Don't build a car behind closed doors, listen to everyone's opinions more.