一筋縄では行かない
(Hitosuji nawa de wa ikanai;
“A single rope won’t do”)

Definition:

A situation that can’t be handled using the ordinary means, or everyday methods. Especially refers to an enemy or opponent who can’t be overcome with one’s usual techniques or strategies.

Breakdown:

We begin three characters in with the noun 縄 (nawa), “rope.” This is modified by number-noun 一筋 (hitosuji), “one strand,” and the resulting noun phrase is followed by the particle で (de), which marks it as the means by which an action is carried out. This entire structure is marked as the topic of discussion by the particle は (wa), and the comment on this topic is the verb 行く (iku), “to go,” in negative conclusive form as 行かない (ikanai). Literally this would be “doesn’t go,” but more figuratively it takes on the meaning “no good,” “useless.”

Notes:

Variants on this phrase may do without the は, or use the archaic negative verb form 行かぬ (ikanu).

This phrase is attributed to a mid-Edo-era joururi play titled 『関取千両幟』 (Sekitori senryou nobori). That said, although it’s not clear from sources currently at hand, the image of ropes seems to be significantly older and related to the tradition of 注連縄 (shimenawa), which are used in Shinto practice to mark and ritually purify a space.

Example sentence:

「このボードゲームはマスターしたつもりだったけど、大学の寮で会った先輩は一筋縄では行かない手強い相手だからもっと深くその作戦が勉強したくなってきた」

(“Kono boodogeemu wa masutaa shita tsumori datta kedo, daigaku no ryou de atta senpai wa hitosuji nawa de wa ikanai tegowai aite dakara motto fukaku sono sakusen ga benkyou shitaku natte kita.”)

[“I thought I’d mastered this board game, but an upperclassman I met at the college dorm is a really strong opponent; I can’t win with my regular play style. It makes me want to study the game’s strategies even more deeply.”]