But a rabbit-hole is just as dangerous.

学びて思わざれば則ち罔し
(Manabite omowazareba sunawachi kurashi;
“Study without consideration is nothing.”)

Definition:

No matter how much you study, if you don’t also think about the content of what you’re learning, you can’t actually reach the truth. Unexamined input is almost useless.

Breakdown:

We begin with the verb 学ぶ (manabu), “to study,” in conjunctive form, which allows it to work with another verb. Accordingly, it’s followed by 思う (omou), “to think,” in imperfective form. This in turn takes the negative suffix ざり (zari) in perfective form, which allows it to take the conditional suffix ば (ba), “when.” The result of the conditional is 則ち (sunawachi), in this case “and then,” and then 罔し (kurashi). This last is not common Japanese these days – in fact, 罔 is a rare character often used to mean “net,” but which can also mean – and apparently originally meant in Chinese – “deceive” or “not.” Anyway, I’m not 100% certain about why there’s that shi on the end. My guess is that it’s an adjective in sentence-final form, equivalent in both form and function to the more prosaic 無し (nashi).

Notes:

This comes to us from Confucius’ Analects (論語, in Japanese Rongo), in the section on governance (為政). It may be followed by counterpoint 思いて学ばざれば則ち殆し (omoite manabazareba sunawachi ayaushi), “Thinking without studying is dangerous” – i.e. simply trying to reason things through on your own without a solid educational background leads to a complacency that leaves you open to all sorts of uncaught errors.

Example sentence:

「先生、教科書をちゃんと読んでもう理解したはずなのに、どうしてエッセイも書かないといけないのですか？」　「考えさせるためだよ。学びて思わざれば則ち罔しというからね」

(“Sensei, kyoukasho wo chanto yonde mou rikai shita hazu na no ni, doushite essei mo kakanai to ikenai no desu ka?” “Kangaesaseru tame da yo. Manabite omowazareba sunawachi kurashi to iu kara ne.”)

[“Teacher, why do I have to write an essay even though I already read and understood the textbook?” “It’s to make you think more about it. They say that learning without thinking comes to naught, after all.”]