(Koketsu ni irazumba koji wo ezu;
“If you don’t go into a tiger’s lair you won’t get a tiger cub.”)
Nothing ventured, nothing gained. You won’t succeed at anything special if you’re not willing to stick your neck out and take some risks. Thinking defensively only prevents loss rather than bringing gains.
There’s some complicated old Japanese here, so buckle your seatbelts, ’cause we’re in for a ride.
虎穴 (koketsu) starts us off gently with a noun, a compound of “tiger” and “hole” which means, logically enough, “tiger den.” The particle に (ni) indicates directionality, … and here our troubles begin. Our fun troubles!
In modern Japanese, the common intransitive version of “enter,” 入る, is pronounced hai.ru, while 入れる (i.reru) is transitive. Here, though, we see the intransitive variant 入る, pronounced i.ru, which is no longer in common usage. The shift from る to ら (.ra) denotes a shift into 未然形 (mizenkei, the “imperfective aspect”), and to this we affix the negative marker ず in 連用形 (renyoukei, “conjunctive mood”). For the rest of the ending, I was tempted at first to get out my chart and try and assemble a construct of contracted or pronunciation-shifted bound particles (like ず). But my sources suggest that it’s actually just the unbound particle は (wa). The structure ずは functions as negative supposition; “if you don’t ~,” and over time underwent a sound change from zu wa to zumba. Stranger things have happened!
A slightly alternate explanation suggests that instead of 連用形, the ず is actually also in 未然形, allowing it to take the hypothetical-marking bound particle ば (which may or may not be related to the use of は cited above). From there the evolution is the same: the negative hypothetical is a little difficult to pronounce, so it shifts from zuba to zumba. And now you know!
What follows is simple in comparison. We have another noun, 虎子 (koji), a tiger cub, marked with the object marker を (wo), and the verb 得 (u), “get,” in negative sentence-final form. Note that because this is a 下二段 (shimo-nidan, literally “down second grade”) verb in the old grammar, the base u changes to e in the 未然形 for the negative ending ず (zu), which is why the modern version 得る can be read as either eru or uru, depending on the situation.
The character 子 can be replaced with 児 without any change in pronunciation or meaning. Either compound (both 虎子 and 虎児) can also be read as koshi.
This phrase, too, traces its origins back to China, in the 5th century CE Book of the Later Han.
(“Koketsu ni irazumba koji wo ezu no kimochi de, kabushiki ichiba ni touki wo suru koto ni shita.”)
[“Thinking ‘nothing ventured, nothing gained,’ I decided to start speculating on the stock market.”]