(Ten shiru chi shiru ware shiru hito shiru;
“Heaven knows; earth knows; oneself knows; people know”)
Secrets and crimes will eventually come to light. Even if you think something is completely hidden, the gods of the heavens and the earth know about it. You know about it, naturally. And anybody else complicit in your misdeed knows about it as well. That’s a lot of room for leaks getting out. So you’d better do things properly and ethically, no matter how well you believe you can hide your crimes.
A little bit of the feel is perhaps captured by the English phrase “Three can keep a secret, if two of them are dead.”
The quadruple-repeated verb phrase at work here is 〇知る, where the 〇 is a noun and 知る (shiru) is the verb “to know.” The four nouns are respectively 天 (ten), “heaven,” 地 (chi), “earth,” i.e. this mortal realm, 我 (ware), “I,” “self,” and 人 (hito), “person,” i.e. people other than oneself, or in this case specifically a second person being addressed.
This phenomenon is also known as the 四知 (shichi), the “four knowings.” Somewhat ironically, a couple of variants exist that add more possible knowings. Other nouns that can be used in place of 人 include 汝 (an archaic character meaning “you,” with several possible pronunciations), and 子 (usually meaning “child” but here also meaning “you,” and pronounced shi). Similarly, 地 can be replaced with 神 (shin), “god(s).” Finally, the whole can be represented in brief by just the first two, “天知る地知る.”
This saying apparently comes from an anecdote in the Book of the Later Han, a history describing several centuries of imperial reigns and biographies of important figures for about the first two centuries CE. A public official tries to bribe the scholar Yang Zhen (楊震), saying “It’s night and we can’t be seen, so nobody will know.” Yang refuses the bribe, replying “Heaven knows, the earth knows, I know, and you know. Don’t say nobody knows.” (Presumably, he follows this up by slipping on a pair of shades and striding off without a backward glance as his would-be buyer explodes in flames.)
(“Naisho dakara daijoubu tte iwarete mo iya da yo. Ten shiru chi shiru darou.”)
[“I don’t like it even if you say we’ll be fine because it’s a secret. The heavens and the earth know too, you know.”]