First of all, the most important point is that the economic foundation determines the superstructure, and the economy often plays a unique role in many aspects. Once you lose your financial resources, many things are out of the question. Then when you enter the society, you lose the financial support your parents have been providing. When you were on campus, your parents provided you with living expenses. At least you don't have to worry about having no money to eat. But when you step into the society and have your own job, especially when your salary is not enough to support your expenses, you will know why society is more cruel than campus.
Secondly, in the campus era, students are the main body, and people of the same age are more or less similar in temperament and ideas, at least they will be easier to communicate, and everyone's quality is not low, so many people will not lie. But after you step into the society and take part in the work, you are surrounded by a group of people who are promoted because of the company's economic interests. These people may intrigue with you because of some economic interests disputes, and may even shoot at the back because of interests. This is also the cruelty of society.
Finally, when you step into the society, it is followed by economic competition. There will be all kinds of relatives who compare you with who can earn more money, and then define who has stronger ability according to how much you earn, which leads to inner imbalance and exclusion, which is also the cruelty of society. Cherish your time at school. Everything outside the campus is different.