老lǎo生shēng常cháng谈tán

Literal: an old scholar's usual talk
Figurative: The same old talk, repeated so often that it adds nothing new; usually said with a touch of disdain, though sometimes with the admission that the worn advice is right.

Where does 老生常谈 come from?

It is documented in the biography of the diviner Guan Lu in the chronicle of the Three Kingdoms. Guan Lu, famous for his predictions, was invited to the home of the senior official He Yan, who wanted to know whether he would rise to the highest offices. Instead of a prophecy, Guan Lu answered with a warning drawn from the classics: a man in high position must act with caution and humility if he means to keep it. Deng Yang, who was there, brushed the advice aside as "the usual talk of an old scholar." Not long after, both men fell in the purge that brought the Sima family to power: the same old talk turned out to be exactly the advice they needed.

Source (出处): 《三国志》

How is 老生常谈 used? Two examples

他tā讲jiǎng的de都dōu是shì老lǎo生shēng常cháng谈tán，没méi什shén么me新xīn东dōng西xi。
It's all the same old talk — there's nothing new in it.
别bié嫌xián这zhè是shì老lǎo生shēng常cháng谈tán，早zǎo睡shuì真zhēn的de有yǒu用yòng。
Don't brush it off as the same old advice — going to bed early really does work.

In Wanyu, all 400 chengyu have audio on every sentence, and you can save them to your decks and review them with spaced repetition. Free.