Scientists who study happiness have evidence (证据) to show that being kind to others can result in happiness. Acts as simple as buying a cup of coffee for someone can lift a person's mood, for example. Everyday life is full of chances for such actions, yet people do not always make the most of them.

In studies, behavioral scientist Nicholas Epley and I examined a possible explanation: people who do kind acts underestimate (低估) how much the ones receiving kindness value their behavior. 

In the experiments (实验), about 1, 000 people were asked to do some actions to make someone else feel good. We asked both the person performing (执行) the kind act and the one receiving it to answer some questions. The performers were asked to report their own experience and to guess how the receivers might feel. We wanted to understand how valuable people considered these acts to be, so both the performer and receiver had to rate (评分) how "big" the act seemed. In all cases, we compared the performer's expectations of the receiver's mood with the receiver's actual (实际的) experience.

For one, both performers and receivers experienced more positive (积极的) moods. For another, the receivers felt much better than the kind performers expected. The receivers also rated these acts as "bigger" than the people performing them did.

At first, we studied acts of the kindness done for familiar people, such as friends, classmates or family. But we found that performers underestimated their positive influences on strangers as well. In one experiment, performers in a public park gave away hot chocolate on a cold winter's day to people that just happened to be nearby. Again, the kind act brought more happiness than the performers expected.

These findings suggest that what might seem small could matter a great deal to the person we do it for. Considering these warm actions can improve our own mood and brighten the day of another person, why not choose kindness when we can?