Today’s expression isn’t ancient Chinese wisdom but a common everyday expression which uses food as a metaphor. Like many other common expressions it consists of three characters. It goes like this (click the image to enlarge):
炒 (chǎo) means to stir-fry, 冷 (lěng) means cold and 饭 (fàn) means rice or food in general. Stir-frying cold rice in China is similar to the concept of reheating leftovers in the west. As a metaphor it means to keep saying or doing the same old things, no coming up with anything new, rehash. It a bit similar to the phrase ‘to sing the same old tune’.
It’s quite useful in a debate, a brainstorming session and many other situations. You can use it also in the negative form like so:
不要再炒冷饭了 – bú yào zài chǎo lěng fàn le – There’s no need to keep singing the same old song.