It's written in the sky: keep your nose out of other people's business
The ancient Chinese constellations system — the equivalent of the zodiacal constellations in Western astronomy — encompasses the “28 mansions,” among them one named Well, or East Well in Chinese, but called Gemini in English.
To the northeast and southeast of the Well, there are two more constellations called North River and South River. The paths of the three never cross.
Accordingly, Chinese speakers have coined the proverb jingshui bufan heshui, or “well water does not mingle with river water.”
jǐng shuǐ bú fàn hé shuǐ
Today, the saying is still in use but is interpreted as “well or underground water doesn’t mix with river or surface water.”
Figuratively, it means that each minds his or her own business. In English, we may also say “you live your life, and I live mine.”
Another widely quoted Chinese expression with a similar meaning reads qiaoguiqiao luguilu, which may be translated directly as “bridges are bridges; roads are roads.”
qiáo guī qiáo lù guī lù
The saying means each going his own way without interfering with one another.
It’s often quoted after two people have a quarrel and decide to split up. One of them may say “from now on, bridges are bridges; roads are roads.” In other words, “from now on, let’s go our separate ways and not bother each other anymore.”
It may also be used when one firmly insists on dealing with two unrelated issues separately.
For example, to seal a business deal with a friend, one may say “bridges are bridges; roads are roads,” meaning friendship is friendship and business is business.