NW Leah v. Keisha/Natalie

I'm interested in the difference between Leah and Natalie. Leah has spent her whole life going against what was expected of her: she did next to nothing with her college degree, is living in a home worse than the one she grew up in, is deciding not to have children. Natalie, on the other hand, has spent her life doing only what was expected of her: went to college, got an excellent job, lives in a nice house, has a family. Leah, however, appears to be more happy with where she is than Natalie. Why is this? This is made more interesting when we take into account the fact that they grew up together and were best friends...many of the things they did, they did together.