I see it, with my children's friends and my relatives. How even children with birth defects and other special needs seem to get steadily pushed toward success, if they are raised by a married couple. Everyone else struggles to not be derailed. They can make it as far, but it requires much more effort and luck, on their part.
Discussion
We've recently had to deal with a death. One of them never managed to get passed the chaos in his home life, unfortunately. He was so promising.