养痈遗患 to harbor a festering sore
Explanation
比喻包庇坏人坏事，结果会遭受祸害。
The idiom refers to the fact that conniving with bad people and bad things will ultimately lead to disaster.
Origin Story
话说东汉时期，有个叫冯衍的人，他曾经写信给他的弟弟，信中告诫弟弟说：『养痈长疽，自生祸殃。』意思是说，如果养着毒疮不去治疗，它会越来越严重，最终会危害自身。这就好比包庇坏人坏事，起初可能觉得没什么，但时间久了，坏人坏事就会变本加厉，最终给自己带来灾难。就像一个国家，如果对一些违法乱纪行为视而不见，任其发展壮大，那么最终受害的还是国家和人民。一个地方，如果对一些社会败类不加处理，任其发展，最终会给社会带来无尽的危害。一个家庭，如果对一些不良习惯不加制止，任其发展下去，那么这个家庭就会走向衰败。 因此，我们对待任何事情都要有担当，对恶势力要坚决打击，不能姑息养奸，否则最终会害人害己。
During the Eastern Han Dynasty, there was a man named Feng Yan, who once wrote a letter to his brother warning him that 'harboring a festering sore will eventually bring disaster upon oneself.' He meant that if you let a poisonous sore fester without treatment, it would become more serious and eventually harm you. This is similar to condoning wrongdoing. At first, it may seem harmless, but over time, the wrongdoing will become more serious and eventually bring disaster. Like a country, if some illegal and disorderly acts are ignored and allowed to grow, the country and people will ultimately suffer. A place, if some social scum are not dealt with, allowed to develop, will ultimately bring endless harm to society. A family, if some bad habits are not stopped, allowed to develop, then this family will decline. Therefore, we should be responsible for everything, and resolutely strike down evil forces, and not condone evil, otherwise, it will eventually harm both others and oneself.
Usage
常用于警示人们不要姑息养奸，要及时处理有害的事物，避免留下后患。
It is often used to warn people not to indulge in evil, but to deal with harmful things in a timely manner to avoid future troubles.
Examples
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他一味地姑息养奸，最终养痈遗患，酿成大祸。
ta yiwei de guxi yangjian, zhongjiu yangyong yihun, niangcheng da huo. zongrong fanzui fenzi, zhihui yangyong yihun, weihai shehui
He indulged in evil and eventually caused great harm.
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纵容犯罪分子，只会养痈遗患，危害社会。
Indulging criminals will only harm society.