Motto is the essence of the wise man's speech, and there is no strictly defined concise sentence as the code of conduct for future generations. As far as the sentence "Young people who don't work hard are sad" is concerned, it comes from Han Yuefu's ancient poem "Long Songs". It is the essence of speech, which is used by later generations to motivate themselves not to miss a good opportunity. It should be said that it is a motto. I wish you health and happiness every day!