expression, noun
having no effect; waste of effort
Idiomatic expression literally meaning 'a clamp on tofu', used to describe a futile or pointless action that produces no result.
彼に注意しても豆腐に鎹だ。
Warning him is like trying to clamp tofu — it's completely useless.
いくら説得しても豆腐に鎹で、彼は聞く耳を持たなかった。
No matter how much I tried to persuade him, it was a waste of effort; he wouldn't listen.
Similar idiom meaning 'a nail into rice bran', also expressing futility, but 豆腐に鎹 specifically evokes the image of clamping something soft and unyielding.
Means 'pushing against a shop curtain', implying no resistance or effect; 豆腐に鎹 focuses more on the impossibility of getting a grip or making an impact.
A traditional Japanese idiom. The exact origin is uncertain, but it draws on the image of trying to fasten soft tofu with a metal clamp, which would simply slip or crush the tofu, symbolizing a futile effort.