Recently, I thought of a rather painful interpersonal phenomenon, and I wonder if you’ve experienced it. You tend to care especially about friends or coworkers, and you help a lot. At first, the other person is grateful—but over time, they start to take your efforts for granted. Even more infuriating is this: the one time you don’t help, the other person gets angry, and may even feel that you’ve changed. I’ve fallen into this trap myself. I once especially wanted to be a “people-pleaser,” only to find that gratitude kept decreasing while everyone else’s expectations kept rising. Later, I finally understood that this isn’t a human-nature problem. It’s a little-known but super important law in psychology—the Weber–Fechner law.

Actually, the Weber–Fechner law is very simple. For any stimulus, we initially have a strong reaction—but if it happens too many times, the brain starts to “get used to it,” and the response gradually becomes weaker. It’s like someone sending you a gift for the first time makes you especially happy; the second time can still move you, but after many times it just feels normal. In neuroscience, this is called “stimulus adaptation,” and it’s also our brain’s energy-saving mode—otherwise, we’d be equally sensitive to everything, and life would have fallen apart long ago.

What’s even more interesting is to look at it from the dopamine perspective. Behavioral rewards initially bring a large amount of dopamine (the kind of brain chemical that makes you feel excited and happy), but your brain’s reward system quickly learns to predict this good thing—so when it really happens, you’re not quite as excited. This is also why the honeymoon period eventually passes: with the same thing, the feeling just isn’t as intense anymore. In economics, it’s called “diminishing marginal utility”—you invest the same amount, the initial return is high, but the more you add later, the smaller the gains you get.

Psychologist Weber even conducted a classic experiment that very well illustrates the issue. He had people hold a 400-gram weight, then changed it to 405 grams. Most people immediately felt that it had become heavier. But if the first weight was 4000 grams and only increased by 5 grams, almost no one could tell the difference. Feeling is fundamentally a relative game. This logic isn’t only applicable to physical sensations; it also applies to interpersonal relationships, consumer psychology, and even habit formation. In 2016, a British psychology magazine published an experiment in which participants received different numbers of “small favors” each day. The results showed that everyone’s sense of novelty about high-frequency rewards disappeared quickly; in contrast, after reducing the frequency of rewards, people valued them more and remembered them more deeply. Think about it—sometimes less really is more.

So how do you reverse this “marginal contribution effect”? First, deliberately control how frequently you give, so that your kindness becomes scarce. Don’t go all-in from the start—especially in newly formed relationships. Low-frequency, high-quality help is far more likely to be appreciated than being available whenever they call. When friends ask for help, occasionally take the initiative, and occasionally say, “This time isn’t really convenient, but I’ll do my best next time.” Paradoxically, the other person may end up re-experiencing the feeling of anticipation.

Second, create small changes to increase unpredictability. Your brain loves the element of surprise. What you need to do isn’t to mechanically repeat the same good deeds, but to periodically switch things up and use different new approaches. Even just changing the way you express care can have particularly noticeable effects in managing relationships, motivating teams, and even parent-child interactions.

Finally, keep your boundaries with grace and learn to refuse appropriately. Every act of kindness should make the other person understand that it isn’t something you can easily come by. Setting boundaries is essentially about maintaining your “psychological threshold” in terms of emotions. As psychologist Timothy Wilson put it well, a sense of boundaries in a relationship is the real kind of lasting love. Even just occasionally saying “no” can keep interactions fresh and respectful.

In the end, don’t treat the Weber–Fechner law as a defensive shield for social interactions. Real pros don’t use it to scheme against others. Instead, they learn to regulate their own sensitivity, give selectively, and put their kindness and energy into the people and things that are truly most worth it. Don’t let your sense of self-worth depend entirely on other people’s feedback, and don’t treat good intentions as “hard currency” that’s always discounted. If you can apply the Weber–Fechner law to self-awareness, every proactive act of kindness will feel more weighty. Carefully manage your giving threshold—be sensitive when you should be, and be relatively numb when you should be. No matter how others respond, it won’t cause your social initiative to slip out of your hands.