Meaning
“Kozo” (conduct) refers to advancing and retreating – that is, how a person acts and decides to carry themselves. “Kiyo” (praise and blame) refers to the judgment others pass on that conduct. What makes this line distinctive is how cleanly it separates the two: the actor has full ownership of their own conduct, while other people have full ownership of their own opinions about it.
The doubled insistence – “it does not involve me, it is no concern of mine” – is not the coldness of someone who simply ignores what others think. It is the practical logic of someone who refuses to let an uncontrollable thing, other people’s judgment, occupy their mind, so that all their attention can go toward the one thing they can control: their own conduct. For Katsu, who was accused of “changing sides” for serving the new government after a lifetime as a shogunate official, this stance was not empty bravado – it was how he took responsibility for a choice he had made.
The episode itself – answering an essay of several hundred words with a single terse sentence – lends the line its force. Responding with action rather than argument, in a way that matched what he actually said, is part of why this reply is still remembered and quoted today.
Lesson for Today
Katsu draws a hard line: other people's judgment is not something you can control, but your own conduct is. The next time someone's words threaten to throw you off balance, try separating the two - "that is their opinion; it is not the same thing as what I actually do." Rather than freezing up out of concern for how you'll be judged, choose the action you believe is right and take ownership of the outcome yourself; in the end, that is what actually moves you forward.
Background
Around 1892, Fukuzawa Yukichi wrote a draft essay, "Yase-gaman no Setsu" ("On Stubborn Perseverance"), criticizing Katsu Kaishu and Enomoto Takeaki - both former shogunate retainers who had gone on to take senior posts in the Meiji government - for lacking the samurai spirit of holding one's ground even in defeat. Fukuzawa sent the draft to both men asking for their response. Enomoto answered at length, but Katsu is said to have replied with only this single, terse sentence. The letters were kept private at first, but in 1901, shortly before Fukuzawa's death, the essay was published in the newspaper Jiji Shinpo as "Yase-gaman no Setsu," and that May it was issued as a book together with Katsu's and Enomoto's replies. The text remains publicly available today through Aozora Bunko, Japan's public-domain digital library.