But there's also a wonderful case for optimism.

So there's the optimism.

But now let's look at the case for optimism. (Laughter)

So optimism changes subjective reality.

I'm going to talk to you about optimism or more precisely, the optimism bias.

That very optimism is uniquely American.

So they have adjusted the 2012 Olympic budget for the optimism bias.

And there are great moments of optimism.

My father chose not to disturb my optimism.

Instead, there was a litany of astonishing optimism.

Come on. Let's keep a little optimism here.

The group of senators doesn't share your optimism.

...Just the perfect combination of optimism and naivety.

In fact if you look at world history you can see some reasons for optimism.

There is considerable optimism that the economy will improve.

So all in all, optimism has lots of benefits.

Perhaps we should say the same thing about optimism.

However, undeterred due to my teenage optimism (Laughter) (Applause)

Certainly, nothing can give you more optimism than that.

But private optimism about our own personal future remains persistent.

Optimism leads to success in academia and sports and politics.

And maybe the most surprising benefit of optimism is health.

Optimism is sometimes characterized as a belief, an intellectual posture.

And I therefore believe that optimism is what drives architecture forward.

And this hope, this optimism, endured a year of turbulent transition.

Right then I felt a sudden burst of joy and optimism,

In fact, without the optimism bias, we would all be slightly depressed.

Secondly, we need to aim off of the optimism of the generals.

Here at the end of round one I'm gonna recommend cautious optimism.

And I think, as you'll see, there's reasons for optimism, because I believe that the best is yet to come.

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

So unrealistic optimism can lead to risky behavior, to financial collapse, to faulty planning.

Recently, Obama has introduced optimism at a sort of time of global financial crisis.

Here are the four things I came up with. The first is urgent optimism.

The day I left home for the first time to go to university was a bright day brimming with hope and optimism.

The day I left home for the first time to go to university was a bright day brimming with hope and optimism.

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

There was an energy there, an implacable optimism, a strange mixture of humility and daring.

The opportunity we're going to look to is a genuine basis for optimism about the bottom billion, and that is the commodity booms.

So what we would really like to do, is we would like to protect ourselves from the dangers of optimism, but at the same time remain hopeful, benefiting from the many fruits of optimism.

The British government, for example, has acknowledged that the optimism bias can make individuals more likely to underestimate the costs and durations of projects.

That proved to be no more than an expression of optimism when World War II began.

Controlled experiments have shown that optimism is not only related to success, it leads to success.

But the good news is that becoming aware of the optimism bias does not shatter the illusion.

Well I've already told you about all of the benefits of the optimism bias, which probably makes you want to hold onto it for dear life.