理り性せいのタガ

expression

the bounds of reason; the limits of common sense

Metaphorical expression likening reason to a barrel hoop that holds things together; often used when someone's self-control or rationality is about to break.

• 怒いかりで理り性せいのタガが外はずれた。

  In anger, the bounds of reason came off.

• 彼かれはいつも冷れい静せいだが、今こん回かいは理り性せいのタガが緩ゆるんだようだ。

  He's usually calm, but this time the limits of his common sense seem to have loosened.