Origin Story
Dogin-gaegin comes from yut, Korea's own traditional board game. On the yut board, the distance over which your piece can catch up to and capture an opponent's piece is called, in pure Korean, a gin. When you toss the yut sticks, a "do" moves one space and a "gae" moves two. So dogin means the distance at which you can capture an opponent's piece with a do, and gaegin the distance you can capture it with a gae. But one space versus two — on the board, that gap is truly trivial. Since it makes little difference whether you capture with a do or a gae, dogin-gaegin came to mean "so alike that the two aren't worth comparing."
It is often written "dojjin-gaejjin" or "dojin-gaejin" as well, where "jin" is a dialectal form of "gin." The standard form is dogin-gaegin, but fittingly for a word born from a game, it has come down to us with many spoken variations.
Meaning Evolution
How It Is Used
This shop or that one, the prices are much of a muchness ("dogin-gaegin").
You both showed up late, so who's blaming who? You're six of one, half a dozen of the other ("dogin-gaegin").
Whichever option you pick, the outcome looks like it'll be about the same ("dogin-gaegin").
Related Words
Memory Hook
On a yut board, capturing from one space (do) or two (gae) comes to the same thing — picture that trivial gap.
"One space or two, on the yut board it all comes out about the same."
