焼け石に水

[yakeishi-ni-mizu]

Literal translation:

(Pouring) water on a heated stone

Meaning:

Ineffective or meaningless effort

Example:

腱鞘炎に対処するために、人間工学キーボードを買ったけど、焼け石に水だった。:

In order to cope with wrist pain, I bought an ergonomic keyboard, but it turned out to be meaningless.

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石 [ishi]: stone

水 [mizu]: water

人間工学 [ningenkougaku]: ergonomics

キーボード: keyboard

買う [kau]: buy, purchase

腱鞘炎 [kenshouen]: wrist pain, tenosynovitis