The "lottery of birth" is like when you play a game with your friend and you pick out of a hat to see who gets which prize. But in this game, you don't get to pick your prize, you just get whatever you happen to pick out of the hat.
When a baby is born, they don't get to choose where or to whom they are born. They just get born into a certain country, family, and social class. This can have a big impact on their life and opportunities.
For example, if you are born in a rich country with lots of resources and good schools, you will have more opportunities than someone born in a poor country with little resources and not many good schools. If you are born into a family with lots of money and connections, you might have an easier time getting a good job or going to a good school compared to someone born into a family that doesn't have those advantages.
So, the lottery of birth is just a way of saying that a person's life is affected by factors that they don't have any control over, like where they were born and who their family is. It's important for us to understand this so we can work to make the world a fairer and more equal place for everyone, no matter where they were born or who their family is.