后患无穷 Endless future troubles
Explanation
指以后的祸害没有个完。比喻事情处理不当，会留下隐患，造成长期的危害。
Refers to future harm without end. A metaphor for the improper handling of things, which will leave hidden dangers and cause long-term harm.
Origin Story
汉献帝建安元年，徐州牧刘备受到袁术的攻击就只身投靠曹操。曹操表面上重用刘备，让刘备招兵买马到徐州去攻打袁绍。谋士郭嘉听说放走了刘备，肯定会后患无穷。曹操立即意识到这一点，就带兵攻打徐州，刘备赶紧投靠了袁绍。这件事告诉我们，处理事情要谨慎，不能留下隐患，否则会造成后患无穷的后果。
In the first year of Emperor Xian's Jian'an reign of the Han Dynasty, Liu Bei, the governor of Xu, was attacked by Yuan Shu and fled to Cao Cao. Cao Cao ostensibly promoted Liu Bei, allowing him to raise an army to attack Yuan Shao. The strategist Guo Jia heard that Liu Bei had been released, and it would inevitably lead to endless future troubles. Cao Cao immediately realized this and led his troops to attack Xu Zhou. Liu Bei quickly sought refuge with Yuan Shao. This event tells us that we should be cautious in dealing with things. We should not leave hidden dangers, otherwise, it will cause endless future troubles.
Usage
常用来形容事情处理不当，会留下隐患，造成长期的危害。多用于贬义。
Often used to describe that improper handling of things will leave hidden dangers and cause long-term harm. Mostly used in a derogatory sense.
Examples
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纵容破坏植被、滥砍乱伐，是后患无穷的事。
zòngróng pòhuài zhíbèi, lànkǎn luànfá, shì hòuhuàn wúqióng de shì.
Tolerating vegetation destruction and excessive deforestation is a matter of endless future troubles.
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如果不及时解决这个问题，将来可能会后患无穷。
rúguǒ bù jíshí jiějué zhège wèntí, jiānglái kěnéng huì hòuhuàn wúqióng.
If this problem is not solved in time, it may lead to endless future troubles in the future.