Meaning: “Advice to him/her is like water sliding off a duck’s back” or “It’s like pouring water into a sieve.”
The word kasugai refers to a clamp tool used for joining together pieces of wood.
Since it is almost pointless to put a block of tofu in a clamp, this proverb means that no matter how much advice you give to a person they won’t accept it.
Rather than tofu in a clamp, it should be tofu in soy sauce, right. It’s also even better if you top the tofu with green onions and ginger.
For this reason, I can’t give up “tofu in soy sauce” as a saying.
There I go. I’m pretty stubborn about this point, so the proverb “tofu ni kasugai” applies to me here.