So, to get things going, I want to ask you a question. The question is, how happy are you? How happy is your life? It's a very vague question but try to answer it in your head. Put it on a scale from one to ten. Now, this question has been asked over and over again across many countries and across thousands, many thousands of people, and almost nobody answers ten. But most people do think that they're substantially happier than the midpoint, common answers are seven and eight. So, one study did this across 42 countries, and they found that none of them had an average happiness under five. In this one study, the most happier were the Swiss, the most miserable were the Bulgarians, and the Americans racked up as pretty happy, on the happy scale. Now, I'm going to use these numbers for a lot of the studies we're going to talk about later on, and it's worthwhile being skeptical as to what these answers can mean. So, I do think that your answer to the question has some real value. It predicts all sorts of aspects of your life. It seems to have real meaning, but at the same time any single reading isn't perfectly reliable and could be swayed by small effects. So, in one study for instance, they tested people on psychology department, and half of the people right before they were asked how happy they were found a dime, the other half didn't. It turned out when asked how good your whole life is, the people who found a dime were happier. In a similar result, people are more positive about their whole life when you ask them on sunny days. When it's a rainy day, people are net less positive about her whole life, unless you remind them of the weather. Once they know about the whether, they can use this information to recalibrate and then they're more accurate. So, what is happiness? Well, we have an evolutionary answer. Happiness for an evolutionary psychologist is a goal-state that animals have evolved to pursue. When you're happy, that means your needs have been satisfied. So, for instance, hunger is unpleasant if you're really hungry or you'll be miserable. But being full is pleasant, and so you're satiated and you're happy. Steve Pinker sums this up quite nicely. He notes, "We are happier when we are healthy, well-fed, comfortable, safe, prosperous, knowledgeable, respected, non-celibate, and loved. If you look in your life and you could tick off all of these things, then my bet is that you are pretty darn happy. But then, Pinker notes himself that it's not quite that simple. There's a couple of reasons why, there's a couple of facts that should shake your perception that happiness is a simple matter. One is that people right now, Americans in the 21st century and I meant many of you from outside United States who are listening to this and watching this, you're healthier, better fed, safer, than just about any other time in history, but you don't seem to be happier. So, it's not like people get progressively happier as their status in life increases, also there are individual differences in happiness. We'd all be in the same community and we all have our basic needs met, but some people are very happy and some people aren't happy at all. To explain these facts and to learn a little bit more about what makes us happy and how happiness works and how one can cultivate happiness in one's life, we need to keep in mind three quite surprising facts about happiness.