Luck (to have to intellect for the training for a well-paid job, for health good enough to work and have children, etc) and I'm sure hard work too.
We all have different balances of luck, in every area of life.
However, it's naive to think anyone has a perfect life. Children might not show any sign of being affected by the divorce until much later on, when they are striking out into the world trying to form their own adult relationships. You have no idea. That's just an example.