空穴来风 Empty cave, wind comes in
Explanation
空穴来风，指消息和谣言的传播不是完全没有原因的。也比喻流言乘机传开来。
Empty cave, wind comes in - This idiom means that rumors and news are not spread without reason. It also means that rumors spread when they have the opportunity.
Origin Story
战国时期，宋玉陪楚顷襄王到兰台游玩，楚王迎着凉风感慨他与百姓共享它，宋玉借风劝谏他说：“枳句来巢，空穴来风”，不同条件会产生不同的风，你的风经过明山秀水是芳香的，百姓身处陋巷混浊之地是腐臭的。
During the Warring States period, Song Yu accompanied King Qing Xiang of Chu on a trip to Lantai. The king, feeling the cool breeze, commented that he shared it with the people. Song Yu, using the wind as a metaphor, advised him, saying: '枳句来巢，空穴来风.' Different conditions produce different winds. Your wind, passing through beautiful mountains and waters, is fragrant, while the wind blowing in narrow alleys and muddy places smells foul.
Usage
空穴来风，这个成语常常用于：1. 指某件事并非空穴来风，一定有其原因。2. 指某件事有可能会发生，需要引起注意。
Empty cave, wind comes in - This idiom is often used to express the following: 1. That something is not without reason. 2. That something may happen and should be paid attention to.
Examples
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网上流传的这些消息，空穴来风，还是小心为妙。
wang shang liu chuan de zhe xie xiao xi, kong xue lai feng, hai shi xiao xin wei miao.
The news circulating online is not without reason, it's better to be careful.
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事情的发生并非空穴来风，一定有其根源
shi qing de fa sheng bing fei kong xue lai feng, yi ding you qi gen yuan
These rumors circulating online are not groundless, you should be careful.