Recently, I’ve been increasingly realizing that understanding human psychology is truly a must-learn subject. No matter whether it’s romance, work, or social interactions, there are always some interesting psychological patterns behind them.

First, let’s talk about romance. The sunk cost fallacy is especially brutal—9 out of 10 people have fallen for it. Even when you clearly know the other person is a bad boy or a bad girl, you still can’t bring yourself to break up. It’s not really because you love them so much, but because you’ve already invested too much, so letting go feels even harder. The higher the cost you’ve paid, the harder it is to escape. The inverse proportional law is also very realistic: when you don’t love him, he loves you the most; once you take the initiative to show weakness, he ends up not cherishing you. So the smartest approach is to stay mysterious and calm—make the other person curious about you, instead of always groveling.

There’s also a harsh truth in human psychology called the peak-end rule. If someone does 99 good things, but only does one bad thing, they are seen as a bad person. Conversely, if someone does 99 bad things, but only does one good thing, other people will treat them as a good person. That’s why first impressions and last impressions are so crucial.

When it comes to human weaknesses, the forbidden fruit effect is especially interesting. The more you try to hide your flaws, the more others pay attention—for example, a receding hairline. The Pandora’s effect also works this way: people have a rebellious mindset of wanting what’s prohibited. The more you don’t let me see it, the more I want to see it. Deep down, people who are more insecure often hope to see others make a fool of themselves. And those who are a failure outside tend to become even more domineering at home.

Human psychology also taught me a very practical technique called the door-in-the-face effect. Once someone agrees to your one seemingly insignificant request, they’re more likely to agree to a bigger request you make afterward. The face-saving effect is similar: you start by making a big request and get rejected, then you follow up with a smaller request, and the other person generally feels too embarrassed to refuse again.

The broken-window effect can be seen everywhere in everyday life. In a clean place, people feel less comfortable littering. But the moment the first piece of trash appears, others will follow suit without hesitation. For any small matter, if you don’t stop it at the beginning, once it becomes the norm, it’s very hard to change. The 12-second effect is also worth noting: the time a person spends being furious about something is only 12 seconds. After that, they usually return to calm. Unfortunately, most people are controlled by those 12 seconds and end up doing things they later regret.

There are also some even more interesting patterns. The bridge-building effect tells us that you can take someone you like to a certain place, then tell her that this is our secret base—this can quickly draw you emotionally closer. The birdcage effect explains why the more we have, the less satisfied we feel. Buying a pair of shoes makes us want matching clothes; the more possessions we have, the stronger our desires become.

The Franklin effect is also worth pondering. People you’ve helped before may not necessarily repay you, but the people you’ve helped often feel more willing to help you again. The generation effect reminds us that learning existing knowledge is far slower than learning through actual practice—only by doing it yourself with your own hands can you truly learn it.

Finally, let me mention the Rosenthal effect. If you’re an introvert and you’re fairly socially anxious, the best way is to label yourself as outgoing during your first self-introduction, because people’s behavior is guided by their awareness. The hippocampus effect is also common: that familiar “it feels like I’ve experienced this before” feeling often comes from the brain recalling a movie or novel you’ve seen earlier. The recency effect is very common in the workplace—people who speak last are often easier to be convinced, and this is also why leaders tend to speak last.

To be honest, studying human psychology in depth is really about learning how to better understand ourselves and others. These patterns aren’t meant to manipulate people; they help us avoid detours in complicated relationships.