顾此失彼 to neglect one thing while trying to handle another
Explanation
形容因忙乱或慌张而不能兼顾，顾了这头，丢了那头。
It describes a situation where one cannot take care of everything at the same time due to rush or nervousness, so one neglects one thing and then another.
Origin Story
话说唐朝时期，有个秀才名叫王小二，他勤奋好学，一心想考取功名。为了节省时间，他每天早上起来，一边读诗，一边吃早饭；一边走路上学，一边背诵课文。可是，他顾此失彼，常常把饭粒撒在书上，也常常忘了背诵什么。考试的时候，他更是顾此失彼，许多题目都不会做，最终落榜。后来，王小二吸取教训，调整学习方法，不再顾此失彼，最终金榜题名。
Once upon a time in ancient China, there was a diligent scholar named Wang Xiaoer, who was determined to pass the imperial examination. To save time, he read poems while having breakfast and recited texts while walking to school every morning. However, he often spilled rice grains on his books and forgot what he had recited due to his lack of focus. During the exam, he was equally unfocused, unable to answer many questions, and ultimately failed. Later, Wang Xiaoer learned his lesson, adjusted his study methods, and stopped being distracted. In the end, he passed the examination with flying colors.
Usage
用来形容做事不能兼顾，顾此失彼，或者忙乱慌张。
It is used to describe that one cannot take care of everything at the same time, or is too busy or nervous.
Examples
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他一心想兼顾事业和家庭，结果顾此失彼，两头落空。
tā yīxīn xiǎng jiāngù shìyè hé jiātíng, jiéguǒ gù cǐ shī bǐ, liǎng tóu luò kōng
He wanted to take care of both his career and family, but he failed to handle them both well, resulting in nothing.
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这次考试，我顾此失彼，很多题目都没来得及做完。
zhè cì kǎoshì, wǒ gù cǐ shī bǐ, hěn duō tímù dōu méi lái de jí zuò wán
In this exam, I lost track of time and was not able to finish many questions.
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他工作总是顾此失彼，所以效率很低
tā gōngzuò zǒngshì gù cǐ shī bǐ, suǒyǐ xiàolǜ hěn dī
He always works in a disorganized way, so he's very inefficient