the optimism bias. It's a cognitive illusion that we've been studying in my lab for the past few years

これから楽観主義についてお話します

and 80 percent of us have it.

より正確に言うと 楽観主義バイアスについてです

It's our tendency to overestimate our likelihood of experiencing good events in our lives

それは認知的錯覚の一種で

and underestimate our likelihood of experiencing bad events

私たちの研究室で ここ数年間 研究してきましたが

So we underestimate our likelihood of suffering from cancer, being in a car accident

80% の人がこのバイアスを持っています

We overestimate our longevity, our career prospects.

私たちは 好ましい出来事が起きる確率を 過大評価し

In short, we're more optimistic than realistic, but we are oblivious to the fact.

好ましくない出来事が起きる確率を

Take marriage for example. In the Western world, divorce rates are about 40 percent.

過小評価する傾向にあります

That means that out of five married couples, two will end up splitting their assets

例えばガンを患う確率だとか

But when you ask newlyweds about their own likelihood of divorce, they estimate it at zero percent

交通事故に遭う確率を 過小評価します

And even divorce lawyers, who should really know better

逆に 長寿やキャリア上の成功の可能性は 過大評価します

hugely underestimate their own likelihood of divorce.

すなわち 私たちは 現実的というよりも楽観的なのですが

So it turns out that optimists are not less likely to divorce

このことに気付いていません

but they are more likely to remarry.

例えば 結婚を例にとりましょう

In the words of Samuel Johnson, "Remarriage is the triumph of hope over experience."

西洋では 離婚率は約40%です

So if we're married, we're more likely to have kids.

つまり 5組の夫婦の内

And we all think our kids will be especially talented.

2組は財産分与を行うことになるということです

This, by the way, is my two-year-old nephew, Guy

しかし 新婚さん達に 自分たちの離婚の可能性を問うと

And I just want to make it absolutely clear that he's a really bad example of the optimism bias

0%だと推定します

because he is in fact uniquely talented.

現実を知っている筈の 離婚専門の弁護士でさえ

And I'm not alone. Out of four British people,

自分たちが離婚することになる確率を かなり過小評価します

three said that they were optimistic about the future of their own families. That's 75 percent.

楽観主義者の離婚率は特に低くはない一方

But only 30 percent said that they thought families in general are doing better than a few generations ago.

再婚率は高いことが分かっています

And this is a really important point, because we're optimistic about ourselves

サミュエル・ジョンソンの言葉を借りると

we're optimistic about our kids, we're optimistic about our families

『再婚とは 経験に対する希望の勝利である』 ということでしょう

but we're not so optimistic about the guy sitting next to us,

（笑い）

and we're somewhat pessimistic about the fate of our fellow citizens and the fate of our country

結婚していれば 子供を持つ可能性も高くなりますね

But private optimism about our own personal future remains persistent.

そして皆 自分の子供には特に才能があると思っています

And it doesn't mean that we think things will magically turn out okay

これは2歳の甥のガイですが

but rather that we have the unique ability to make it so.

誤解がないように 明らかにしておきたいのですが

Now I'm a scientist, I do experiments. So to show you what I mean

彼は楽観主義バイアスとしては例外中の例外です

I'm going to do an experiment here with you. Okay.

だって特別に才能があるんですよ

So I'm going to give you a list of abilities and characteristics,

（笑い）

and I want you to think for each of these abilities where you stand relative to the rest of the population.

そして私に限ったことではありません

The first one is getting along well with others. Who here believes they're at the bottom 25 percent?

英国人の4人に3人は

Okay, that's about 10 people out of 1,500. Who believes they're at the top 25 percent?

自分たちの家族の将来は明るいと答えています

That's most of us here. Okay, now do the same for your driving ability.

75%ですよ

How interesting are you? How attractive are you?

しかし 一般的な家庭が

How honest are you? And finally, how modest are you?

数世代前に比べて豊かになったと答えたのは

So most of us put ourselves above average on most of these abilities.

たった30%でした

Now this is statistically impossible. We can't all be better than everyone else.

これは重要なポイントです

But if we believe we're better than the other guy,

私たちは自分自身ついては楽観的です

well that means that we're more likely to get that promotion, to remain married,

自分の子供たちについても然り

because we're more social, more interesting.

自分の家族についても然りです

And it's a global phenomenon. The optimism bias has been observed in many different countries

しかし 隣に座っている他人に関しては楽観的ではなく

in Western cultures, in non-Western cultures

他の市民や国の将来についても

in females and males, in kids, in the elderly. It's quite widespread.

どちらかというと悲観的です

But the question is, is it good for us? So some people say no

にもかかわらず 自分自身の将来に対する楽観主義は

Some people say the secret to happiness is low expectations

根強く 揺らぎません

I think the logic goes something like this: If we don't expect greatness,

それも 魔法によって良い結果がもたらせられると 思っている訳ではなく

if we don't expect to find love and be healthy and successful,

自分たちにその結果を生み出す能力が 備わっていると思っているのです

well we're not going to be disappointed when these things don't happen.

私は科学者なので 実験をしてみましょう

And if we're not disappointed when good things don't happen, and we're pleasantly surprised when they do, we will be happy.

私が主張していることを説明するために

So it's a very good theory, but it turns out to be wrong for three reasons

皆さんと一緒に 実験をしてみましょう

Number one: Whatever happens, whether you succeed or you fail, people with high expectations always feel better.

能力や特徴を いくつかリストアップしますので

Because how we feel when we get dumped or win employee of the month depends on how we interpret that event.

みなさん ひとつひとつの能力に関して

The psychologists Margaret Marshall and John Brown studied students with high and low expectations.

人口全体と比較して どの程度の レベルかを考えてください

And they found that when people with high expectations succeed, they attribute that success to their own traits.

まずは「社交性」です

I'm a genius, therefore I got an A, therefore I'll get an A again and again in the future

社交性が下位25%だと思う人は 手をあげてください

When they failed, it wasn't because they were dumb, but because the exam just happened to be unfair.

そうですね 1,500人中10人というところでしょうか

Next time they will do better. People with low expectations do the opposite.

上位25%だと思う人は？

So when they failed it was because they were dumb

ほとんど全員ですね

and when they succeeded it was because the exam just happened to be really easy. Next time reality would catch up with them. So they felt worse.

同じように 運転のスキルについて考えてください

Number two: Regardless of the outcome, the pure act of anticipation makes us happy.

自分がどれくらい面白いか？

The behavioral economist George Lowenstein asked students in his university to imagine getting a passionate kiss from a celebrity

どれくらい魅力的か？

any celebrity.

どれくらい正直か？

Then he said, "How much are you willing to pay to get a kiss from a celebrity if the kiss was delivered immediately

最後に どれくらい謙虚か？

in three hours, in 24 hours, in three days, in one year, in 10 years?

私たちのほとんどは これらの能力について

He found that the students were willing to pay the most not to get a kiss immediately, but to get a kiss in three days

平均より上に自分を位置づけます

they were willing to pay extra in order to wait

統計学的にはありえませんね

Now they weren't willing to wait a year or 10 years; no one wants an aging celebrity

全員が全員より能力が高いというのは無理なのですから

But three days seemed to be the optimum amount.

（笑い）

So why is that? Well if you get the kiss now, it's over and done with

しかし隣の誰かと比べて 優位だと信じていれば

But if you get the kiss in three days, well that's three days of jittery anticipation, the thrill of the wait.

仕事や結婚で成功する可能性は高くなります

The students wanted that time to imagine where is it going to happen, how is it going to happen.

他の人よりも社交的で面白いのですから

Anticipation made them happy.

これは世界共通の現象です

This is, by the way, why people prefer Friday to Sunday

この楽観主義バイアスは 幅広く確認されています

It's a really curious fact, because Friday is a day of work and Sunday is a day of pleasure,

多くの異なる国々で

so you'd assume that people will prefer Sunday, but they don't.

西洋文化、非西洋文化ともに

It's not because they really, really like being in the office and they can't stand strolling in the park or having a lazy brunch.

男女ともに

We know that, because when you ask people about their ultimate favorite day of the week,

子供からお年寄りに至るまで

surprise, surprise, Saturday comes in at first, then Friday, then Sunday. People prefer Friday because Friday brings with it the anticipation of the weekend ahead

とても普遍的です

all the plans that you have. On Sunday, the only thing you can look forward to is the work week.

これが私たちにとって良いことなのでしょうか？

So optimists are people who expect more kisses in their future, more strolls in the park.

「ノー」という人もいます

And that anticipation enhances their wellbeing

幸福の秘訣は

In fact, without the optimism bias, we would all be slightly depressed. People with mild depression, they don't have a bias when they look into the future

低い期待を持つことだ と唱える人もいます

They're actually more realistic than healthy individuals.

彼らの論理はこんな感じです

But individuals with severe depression, they have a pessimistic bias.

多くを期待しなければ

So they tend to expect the future to be worse than it ends up being.

愛と健康と成功が 手に入ると期待しなければ

So optimism changes subjective reality. The way we expect the world to be changes the way we see it.

手に入らなかった時に 落胆せずに済みます

But it also changes objective reality. It acts as a self-fulfilling prophecy.

良い事が起きなかったときには 落胆せず

. And that is the third reason why lowering your expectations will not make you happy.

良い事が起きた時には 驚き喜べば

Controlled experiments have shown that optimism is not only related to success

幸せになれる という考え方です

it leads to success. Optimism leads to success in academia and sports and politics.

なかなか良い理論に聞こえますが

And maybe the most surprising benefit of optimism is health. If we expect the future to be bright, stress and anxiety are reduced.

3つの理由により間違っているということが 分かっています

So all in all, optimism has lots of benefits.

第一に 結果がどうであっても 成功しても失敗しても

But the question that was really confusing to me was, how do we maintain optimism in the face of reality?

期待が高い人の方が 常に幸福度は高いのです

As an neuroscientist, this was especially confusing, because according to all the theories out there

何故ならば 恋人に振られたり 会社で賞をもらった時に どのように感じるかは

when your expectations are not met, you should alter them.

その出来事をどう解釈するかによるからです

But this is not what we find

心理学者のマーガレット・マーシャルと ジョン・ブラウンは

We asked people to come into our lab in order to try and figure out what was going on.

期待の高い生徒と 低い生徒を比較してみました

We asked them to estimate their likelihood of experiencing different terrible events in their lives

期待が高い生徒が成功すると

So, for example, what is your likelihood of suffering from cancer?

その原因を自分の才能によるものとします

And then we told them the average likelihood of someone like them to suffer these misfortunes.

「僕は天才だからAを取ったし

So cancer, for example, is about 30 percent. And then we asked them again, "How likely are you to suffer from cancer?"

これからもずっとAを取り続ける」

What we wanted to know was whether people will take the information that we gave them to change their beliefs.

失敗しても それは頭が悪いからではなく

And indeed they did -- but mostly when the information we gave them was better than what they expected.

たまたま試験が不公平だったからであり

So for example, if someone said, "My likelihood of suffering from cancer is about 50 percent,"

次回の成績はもっと良くなると考えます

and we said, "Hey, good news. The average likelihood is only 30 percent," the next time around they would say

期待が低い生徒はその反対です

Well maybe my likelihood is about 35 percent." So they learned quickly and efficiently.

失敗したのは頭が悪いからであり

But if someone started off saying, "My average likelihood of suffering from cancer is about 10 percent,"

成功した場合は

and we said, "Hey, bad news. The average likelihood is about 30 percent," the next time around they would say

試験がたまたま簡単過ぎたからというだけで

Yep. Still think it's about 11 percent

次回は現実が待っている と考えます

So it's not that they didn't learn at all -- they did

どっちにしても比較的不幸に感じています

but much, much less than when we gave them positive information about the future

第二に 結果の良し悪しに関わらず

And it's not that they didn't remember the numbers that we gave them;

何かを心待ちにしているだけで幸せに感じるからです

everyone remembers that the average likelihood of cancer is about 30 percent and the average likelihood of divorce is about 40 percent

行動経済学者のジョージ・ローウェンスタインは

But they didn't think that those numbers were related to them.

彼の大学の生徒に聞きました

What this means is that warning signs such as these may only have limited impact

好きな有名人の誰かと情熱的なキスができるとたら

Yes, smoking kills, but mostly it kills the other guy.

その有名人とのキスのために

What I wanted to know was what was going on inside the human brain that prevented us from taking these warning signs personally

どれくらいのお金を払いますか？

. But at the same time, when we hear that the housing market is hopeful, we think

もし今すぐにキスをするとしたら？

Oh, my house is definitely going to double in price

3時間後 24時間後 3日後

To try and figure that out, I asked the participants in the experiment to lie in a brain imaging scanner

1年後 あるいは10年後の場合は？

It looks like this. And using a method called functional MRI

生徒たちが最も多くお金を払うと答えたのは

we were able to identify regions in the brain that were responding to positive information.

すぐにキスする場合ではなく

One of these regions is called the left inferior frontal gyrus

3日後のキスだったのです

So if someone said, "My likelihood of suffering from cancer is 50 percent

待つことに対して より多く対価を払う意思があったのです

and we said, "Hey, good news. Average likelihood is 30 percent,"

まず 1年や10年も待つつもりは無かったみたいですね

the left inferior frontal gyrus would respond fiercely

だって年老いた有名人はいやでしょうから

And it didn't matter if you're an extreme optimist, a mild optimist or slightly pessimistic,

しかし3日間というのは最適な待ち時間のようでした

everyone's left inferior frontal gyrus was functioning perfectly well, whether you're Barack Obama or Woody Allen.

なぜでしょうか？

On the other side of the brain, the right inferior frontal gyrus was responding to bad news

今すぐキスをしてしまったら それで終わりです

And here's the thing: it wasn't doing a very good job

しかし3日後のキスであれば

The more optimistic you were, the less likely this region was to respond to unexpected negative information

3日間 じらされるような期待感と 待たされるスリルが味わえます

And if your brain is failing at integrating bad news about the future, you will constantly leave your rose-tinted spectacles on.

生徒たちは想像する時間がほしかったのです

So we wanted to know, could we change this?

どこでキスされるのだろう

Could we alter people's optimism bias by interfering with the brain activity in these regions?

どんな感じにキスされるんだろう と

And there's a way for us to do that.

期待感で幸せになるのです

This is my collaborator Ryota Kanai.

皆さんが 日曜日よりも金曜日の方が 好きなのも同じ理由です

And what he's doing is he's passing a small magnetic pulse through the skull of the participant in our study into their inferior frontal gyrus.

本当に興味深い事実ですよね

And by doing that, he's interfering with the activity of this brain region for about half an hour

だって金曜日は働く日で 日曜日は遊ぶ日なのですから

After that everything goes back to normal, I assure you.

当然 人々は日曜日の方が嬉しいと思いますよね

So let's see what happens. First of all, I'm going to show you the average amount of bias that we see.

でも違います

So if I was to test all of you now, this is the amount that you would learn more from good news relative to bad news.

これは オフィスに居るのが大好きだとか

Now we interfere with the region that we found to integrate negative information in this task, and the optimism bias grew even larger.

公園を散歩するのが大嫌いだとか

We made people more biased in the way that they process information.

まったりしたブランチが大嫌いということではありません

Then we interfered with the brain region that we found to integrate good news in this task, and the optimism bias disappeared

なぜなら みなさんに

We were quite amazed by these results because we were able to eliminate a deep-rooted bias in humans.

1週間の内で本当に好きな曜日を尋ねると

And at this point we stopped and we asked ourselves, would we want to shatter the optimism illusion into tiny little bits?

予測通り 土曜日が一番人気でした

If we could do that, would we want to take people's optimism bias away?

その次に金曜日 それから日曜日です

Well I've already told you about all of the benefits of the optimism bias,

みなさんが金曜日が好きなのは

which probably makes you want to hold onto it for dear life. But there are,

金曜日にはその後に続く週末や

of course, pitfalls, and it would be really foolish of us to ignore them.

計画していることへの期待感があるからです