The Easterlin Paradox is when people feel less happy, even when they have more money.
Let's say Sally has a bike, and Sally is happy. But then her neighbor, Sarah, gets a new bike that's faster and fancier than Sally's. Suddenly, Sally is not as happy with her bike even though it's the same bike she was happy with before Sarah got her new one.
The Easterlin Paradox is kind of like that, but with money. Researchers found that people in countries that are rich and have high incomes are not necessarily happier than people in countries that are poor and have low incomes. In fact, sometimes people in poor countries are even happier than people in rich countries!
This is a paradox because we might think that having more money would automatically make us happier, but it doesn't always work that way. Instead, happiness seems to depend on how much money we have in comparison to the people around us. If we're always comparing ourselves to people who have more, we might never be truly happy with what we have.