“Research shows that once one is able to provide for basic physical needs (food, shelter, and so on), the correlation between happiness and worldly success quickly approaches zero. So if you’re starving and living on the street in the middle of India, an extra ten thousand dollars a year would affect your happiness a lot. But if you’re sitting pretty in the middle class in a developed country, an extra ten thousand dollars per year won’t affect anything much—meaning that you’re killing yourself working overtime and weekends for basically nothing.”