Another way to think about it is an inheritance. Grandpa has $10B to pass down, but he plans to give equal parts to all his grand-kids. For each new cousin I get, I lose millions. )-; and I gain a new cousin!
The world is a little different, in that grandpa's fortune goes up and down all the time, and his grand kids run the family business, so depending on the cousin, you might be really happy they came along, even in financial terms.