go in one ear and out the other idiom informal
左耳朵进右耳朵出;当作耳边风
If you say that something you hear goes in one ear and out the other, you mean you quickly forget it.
If I have to listen to something I don't understand, it just goes in one ear and out the other. 要是非得让我听我不懂的事情，那也只是左耳朵进右耳朵出。