On the game table of society, there are three types of people who die the fastest: the first are fools who treat everyone as friends; the second are fools who believe that "good will be rewarded"; the third are cowards who never dare to flip the table. Truly tough characters usually stay calm and collected, and a single "no" at a critical moment can silence the entire room instantly. Because they know: the bottom line isn't something drawn on the ground for others to step on, but something hanging overhead that makes people afraid. You can keep your inner softness, but you must grow external armor; you can believe in the light of human nature, but you must also anticipate the darkness of people's hearts. When you learn to say "no" at the right time, you'll discover a magical reality: those who once looked down on you suddenly learn to be polite; those who habitually take advantage start to respect boundaries. It's not that they have changed for the better, but that you have finally grown up. Remember this bloody truth of human nature: the world won't be gentle to you just because you're kind, but it will be courteous because you're not to be messed with. This is the most decent way for an adult to survive!