We have already seen that Sidgwick’s principle of universal benevolence requires us to give no more weight to our own interests than we give to the similar interests of everyone else. Such a principle is unlikely to have been selected for by an evolutionary process; on the contrary, it is exactly the kind of principle that you would expect evolution to select against, because evolution selects for principles that confer advantages on us, our kin, those with whom we are in reciprocally beneficial relationships, and perhaps other members of our small tribe or social group. The need for reciprocity and trust within our social group may well have led to the evolution of a sense of fairness, but the impetus to extend that sense beyond our own group is unlikely to be an evolved automatic response. It is more likely to require the use of our ability to reason. Our reasoning is, of course, a product of evolution, for it enhances our prospects of surviving and reproducing; but it also brings with it the ability to understand things that have nothing to do with evolutionary fitness, such as the ability to do higher mathematics. Perhaps it also brings with it our ability to see that our own interests are no more significant than those of other beings who can enjoy life as much as we can, and can suffer as much as we can. If this is right, the rational basis of Sidgwick’s principle of benevolence is immune from evolutionary debunking arguments, and hence remains standing when these arguments undermine the grounds for accepting non-consequentialist intuitions.Katarzyna de Lazari-Radek & Peter Singer. 2017. Utilitarianism: A Very Short Introduction
我们先来看一看 Emily 的开场白：
I used to think the whole purpose of life was pursuing happiness. Everyone said the path to happiness was success, so I searched for that ideal job, that perfect boyfriend, that beautiful apartment. But instead of ever feeling fulfilled, I felt anxious and adrift. And I wasn’t alone; my friends — they struggled with this, too.
后来 Emily 就去学习积极心理学（positive psychology），读了很多心理学、神经科学和哲学的书——恰好也是我最感兴趣的三个领域。她发现，数据显示，追求快乐反而让人不快乐，尽管大家的生活条件越来越好，但抑郁、甚至自杀的人却越来越多。而研究认为这并不是因为他们缺少快乐，而是缺少生活的意义。于是 Emily 开始追问快乐（being happy）和生活的意义（having meaning in life）有什么区别。
Many psychologists define happiness as a state of comfort and ease, feeling good in the moment. Meaning, though, is deeper. The renowned psychologist Martin Seligman says meaning comes from belonging to and serving something beyond yourself and from developing the best within you. Our culture is obsessed with happiness, but I came to see that seeking meaning is the more fulfilling path. And the studies show that people who have meaning in life, they’re more resilient, they do better in school and at work, and they even live longer.
接下来的演讲就是 Emily 分享自己找到的怎样寻求人生意义的四种方式（four pillars of a meaningful life）：归属感（belonging）、目的（purpose）、超越（transcendence）、讲故事（storytelling）。Emily 的确讲了很多故事，四种方式各讲了一个故事，讲完还继续讲了自己的故事和父亲的故事。这里就暂且略过。最后她总结到：快乐的感觉有来有去捉摸不定，意义才能让我们掌握人生（Happiness comes and goes. But when life is really good and when things are really bad, having meaning gives you something to hold on to）。
我觉得虽然这是一场 TED 演讲，但其实论证方式特别像心灵鸡汤。我直奔主题，我们思考一下，Emily 的演讲从头到尾证明的是在人生中除了快乐之外还有其他重要之事（there’s more to life than being happy）吗？或者说她证明的是追求快乐反而会让人不快乐吗？
回到 Emily 的开场白，谁说追求快乐就一定等同于追求世俗意义的成功呢？Emily 和她的朋友追求好工作、好伴侣、好房子没有获得满足，最多只能证明这些追求快乐的途径可能有问题，但并不能证明「追求快乐」本身有问题，不能证明「 不应该追求快乐」。Emily 说自己通过追求这些没有获得满足，感到焦虑和迷茫，也就是追求某些目标让人感到不快乐，可以得出的结论应该是：这些具体目标，或者追求这些目标的方式方法可能不太对。也许我们追求另外一些目标更容易获得快乐，也许同样是追求这些目标，但换其他一些追求方式我们更容易获得快乐。你不能把自己原以为的那些目标直接等同于快乐本身，然后一起否定掉。
最近一直在读之前提到的 The Book of Why，我觉得 collider 的概念可能是这本书里最重要的几个概念之一。本来我也可以用自己的语言写一个介绍，但好像懒得动笔，就节选书中几段话放在这里（顺序是我刻意安排的）。
X 与 Y 相关的三种解释：
- X 是 Y 的原因；
- X 和 Y 有共同的原因；
We live our lives as if the common cause principle were true. Whenever we see patterns, we look for a causal explanation. In fact, we hunger for an explanation, in terms of stable mechanisms that lie outside the data. The most satisfying kind of explanation is direct causation: X causes Y. When that fails, finding a common cause of X and Y will usually satisfy us. By comparison, colliders are too ethereal to satisfy our causal appetites.Judea Pearl. 2018. The Book of Why. Chapter 6
A→B←C. This is the most fascinating junction, called a “collider.” Felix Elwert and Chris Winship have illustrated this junction using three features of Hollywood actors: Talent→Celebrity←Beauty. Here we are asserting that both talent and beauty contribute to an actor’s success, but beauty and talent are completely unrelated to one another in the general population.
We will now see that this collider pattern works in exactly the opposite way from chains or forks when we condition on the variable in the middle. If A and C are independent to begin with, conditioning on B will make them dependent. For example, if we look only at famous actors (in other words, we observe the variable Celebrity = 1), we will see a negative correlation between talent and beauty: finding out that a celebrity is unattractive increases our belief that he or she is talented.
This negative correlation is sometimes called collider bias or the “explain-away” effect. For simplicity, suppose that you don’t need both talent and beauty to be a celebrity; one is sufficient. Then if Celebrity A is a particularly good actor, that “explains away” his success, and he doesn’t need to be any more beautiful than the average person. On the other hand, if Celebrity B is a really bad actor, then the only way to explain his success is his good looks. So, given the outcome Celebrity = 1, talent and beauty are inversely related—even though they are not related in the population as a whole. Even in a more realistic situation, where success is a complicated function of beauty and talent, the explain-away effect will still be present. This example is admittedly somewhat apocryphal, because beauty and talent are hard to measure objectively; nevertheless, collider bias is quite real, and we will see lots of examples in this book.Judea Pearl. 2018. The Book of Why. Chapter 3
另外两个 collider 的例子：
Try this experiment: Flip two coins simultaneously one hundred times and write down the results only when at least one of them comes up heads. Looking at your table, which will probably contain roughly seventy-five entries, you will see that the outcomes of the two simultaneous coin flips are not independent. Every time Coin 1 landed tails, Coin 2 landed heads. How is this possible? Did the coins somehow communicate with each other at light speed? Of course not. In reality you conditioned on a collider by censoring all the tails-tails outcomes.Judea Pearl. 2018. The Book of Why. Chapter 6
The correlation we observe is, in the purest and most literal sense, an illusion. Or perhaps even a delusion: that is, an illusion we brought upon ourselves by choosing which events to include in our data set and which to ignore. It is important to realize that we are not always conscious of making this choice, and this is one reason that collider bias can so easily trap the unwary. In the two-coin experiment, the choice was conscious: I told you not to record the trials with two tails. But on plenty of occasions we aren’t aware of making the choice, or the choice is made for us.
The distorting prism of colliders is just as prevalent in everyday life. As Jordan Ellenberg asks in How Not to Be Wrong, have you ever noticed that, among the people you date, the attractive ones tend to be jerks? Instead of constructing elaborate psychosocial theories, consider a simpler explanation. Your choice of people to date depends on two factors: attractiveness and personality. You’ll take a chance on dating a mean attractive person or a nice unattractive person, and certainly a nice attractive person, but not a mean unattractive person. It’s the same as the two-coin example, when you censored tails-tails outcomes. This creates a spurious negative correlation between attractiveness and personality. The sad truth is that unattractive people are just as mean as attractive people—but you’ll never realize it, because you’ll never date somebody who is both mean and unattractive.Judea Pearl. 2018. The Book of Why. Chapter 6
[I]n a collider, A→B←C, exactly the opposite rules hold. The variables A and C start out independent, so that information about A tells you nothing about C. But if you control for B, then information starts flowing through the “pipe,” due to the explain-away effect.Judea Pearl. 2018. The Book of Why. Chapter 4
以下摘自《纽约时报》今年 1 月底的报道：
Students have long requested that Yale offer a course on positive psychology, according to Woo-Kyoung Ahn, director of undergraduate studies in psychology, who said she was “blown away” by Dr. Santos’s proposal for the class.
本科生心理研究主任 Woo-Kyoung Ahn 表示，长期以来，学生们一直要求耶鲁开设一门积极心理学课程。她说，桑托斯博士提出开设这门课程时，她「特别高兴」。
Administrators like Dr. Ahn expected significant enrollment for the class, but none anticipated it to be quite so large. Psychology and the Good Life, with 1,182 undergraduates currently enrolled, stands as the most popular course in Yale’s 316-year history. The previous record-holder — Psychology and the Law — was offered in 1992 and had about 1,050 students, according to Marvin Chun, the Yale College dean. Most large lectures at Yale don’t exceed 600.
安博士等管理人员预计这门课的选修人数会很多，但谁也没预料到会这么多。「心理学与美好生活」这门课目前有 1182 名本科生选修，成为耶鲁大学 316 年历史上最受欢迎的课程。耶鲁学院的院长 Marvin Chun 表示，此前的纪录保持者是 1992 年推出的「心理学和法律」课程，约有 1050 名学生选修。耶鲁的大多数大型课程的选修人数都不超过 600 人。Yale’s Most Popular Class Ever: Happiness
Google 了一下发现这门课已经上线 Coursera（《纽约时报》今年 1 月底报道这门课的时候还只是说很快就会上线）。最近几年觉得国内上 Coursera 的网络状况真的不太好，当然我也不是随时都在测试，毕竟试过几次感觉很糟糕之后就不会太有动力去听课了。但今天的网络效果很好，不知道是不是最近用了另一家代理服务……
附一封 Santos 老师的欢迎信：
Congratulations on taking part in this journey! Over the next several weeks, we’ll explore what new results in psychological science teach us about how to be happier, how to feel less stressed, and how to flourish more. We’ll then have a chance to put these scientific findings into practice by building the sorts of habits that will allow us to live a happier and more fulfilling life.
In Spring 2018, I taught “Psychology and the Good Life” for the first time. I created this Yale course because I was worried about the levels of student depression, anxiety, and stress that I was seeing as a Professor and Head of College at Yale. I originally developed this course to teach Yale students how the science of psychology can provide important hints about how to make wiser choices and how to live a life that’s happier and more fulfilling. Since I’m not an expert on positive psychology, I began by learning more about this topic, diving into the work of pioneering scientists like Martin Seligman, Ed Diener, Barbara Fredrickson, Sonja Lyubomirsky, Mihaly Csikszentmihalyi, Daniel Gilbert, Robert Emmons, and others. I also learned more about work in social psychology and behavior change, including work by scholars such as Liz Dunn, Mike Norton, Nick Epley, Gabriele Oettingen, and others. The Yale course was my attempt at synthesizing work in positive psychology along with the science of behavior change. My goal was to present these scientific findings in a way that made it clear how this science could be applied in people’s daily lives.
When I first developed the class, I had no idea it would become the most popular class ever taught at Yale University. The Yale class was featured in both the national and international news media, and I was flooded with requests from people around the world to find a way to share the content of this Yale class more broadly.
This Coursera class is an attempt to do just that. My goal is to share the insights from that popular Yale class with learners far beyond Yale. To make the lectures feel more intimate, we filmed at my home in one of Yale’s residential colleges with a small group of Yale students in the audience. I hope you’ll enjoy this more personal format, which allows you to hear the sorts of questions Yale students had about the material and how they applied the science in their daily lives. We understand that many of you taking the course are not currently college students, but we hope you see yourselves as though you are part of this virtual classroom.
During this course, you’ll have the opportunity to enhance your own well-being by implementing a few simple research-based methods to your own life.
I am thrilled to share this information with a wider audience. As you go through the lessons please share your feedback with the course team! You can direct item-specific feedback via content flags and general course feedback in the Discussion Forums or in the post-course survey when you complete the course.