老于世故 experienced in the ways of the world
Explanation
老于世故指人对社会有深刻的了解和丰富的经验，为人处世老练，精明。
The idiom "Lao Yu Shi Gu" means that a person has a deep understanding and rich experience of society and is sophisticated and shrewd in dealing with people.
Origin Story
年轻的书生李白初入长安，怀揣着满腔抱负，渴望建功立业。然而，面对复杂的人情世故，他屡屡受挫。一次，他兴致勃勃地向一位老臣献策，却因措辞不当，被老臣轻蔑地一笑而过。老臣见他一脸茫然，便语重心长地说："年轻人，你才华横溢，但还不老于世故，在官场中，言语、行动都要谨慎，否则容易吃亏。"李白听后，深感羞愧，从此更加细心观察，认真学习，逐渐成长为一个老于世故的成熟官员。
The young scholar Li Bai, upon first arriving in Chang'an, was full of ambition and eager to make a name for himself. However, in the face of complex social customs, he repeatedly suffered setbacks. Once, he enthusiastically presented a proposal to an old official, but due to inappropriate wording, he was dismissed with a contemptuous smile. Seeing his puzzled expression, the old official said earnestly, "Young man, you are talented, but not yet experienced in the ways of the world. In the officialdom, words and actions must be cautious, otherwise you will easily suffer losses." Li Bai, deeply ashamed, became more observant and studious, gradually maturing into a sophisticated and experienced official.
Usage
用于形容一个人在社会上摸爬滚打多年，积累了丰富的经验，对人情世故有深刻的理解。
Used to describe a person who has been working hard in society for many years, has accumulated rich experience, and has a deep understanding of human relationships and social customs.
Examples
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他老于世故，一眼就看穿了我的心思。
tā lǎo yú shìgù, yī yǎn jiù kàn chuān le wǒ de xīnsī
He is experienced in the ways of the world, and he saw through my thoughts at a glance.
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老于世故的他，轻易不会上当。
lǎo yú shìgù de tā, qīngyì bù huì shàngdàng
The experienced man would not be easily fooled.
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与他共事，要小心，他老于世故，城府很深。
yǔ tā gòngshì, yào xiǎoxīn, tā lǎo yú shìgù, chéngfǔ hěn shēn
When working with him, be careful, he is experienced in the ways of the world and very deep.