画虎不成 painting a tiger but making it look like a dog
Explanation
比喻做事好高骛远，结果一无所成，反而成为笑柄。
This idiom is used to describe someone who sets their sights too high and ends up achieving nothing, becoming a laughingstock.
Origin Story
东汉时期，名将马援教育子侄要学习杜季良和龙伯高，告诫他们如果学不成，就像画虎不成反类狗一样。这个故事反映了马援严谨的治家理念，希望后辈们脚踏实地，有所成就，切勿好高骛远。
During the Han Dynasty, the famous general Ma Yuan educated his nephews to learn from Du Jiliang and Long Bogao, warning them that if they failed, they would be like painting a tiger and instead making it look like a dog. This story reflects Ma Yuan's rigorous family concept, hoping that his descendants will be down-to-earth and achieve something, and not set their sights too high.
Usage
用于形容做事好高骛远，结果一无所成，反而成为笑柄。
It is used to describe someone who is ambitious but ultimately fails, becoming a laughingstock.
Examples
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他学画画，画虎不成反类犬，真是弄巧成拙。
tā xué huà huà, huà hǔ bù chéng fǎn lèi quǎn, zhēn shì nòng qiǎo chéng zhuō
He learned painting, painted a tiger but it looked like a dog, which was a case of trying to be clever and ending up stupid.
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这次的尝试虽然失败了，但至少我们知道了画虎不成反类犬的道理
zhè cì de chángshì suīrán shībài le, dàn zhìshǎo wǒmen zhīdào le huà hǔ bù chéng fǎn lèi quǎn de dàolǐ
Although this attempt failed, at least we know the meaning of 'painting a tiger but making it look like a dog'.