Mathinna's fate really bothered me a lot. She was very intelligent and talented, and I would have liked her to have tried to make more of her life. Although, of course, that's not how it works in the real world - intelligent, talented people end up in dire straights every day - so her fate was certainly realistic.
I think chance does play a pretty big role in one's success or failure in life. Some individuals can overcome the bad things that have happened to them, some not. In my misspent youth, for example, I recall driving while under the influence. I'm horrified about that now, and I realize how incredibly lucky I was to not have been arrested or worse. The same is true of some ill-advised sexual encounters when I was first exploring; I was very lucky not to have gotten pregnant. Either getting arrested or pregnant would have set my life on a completely different trajectory, so yes, I do think chance plays a big role.
I think, though, that we also have the ability to let a bad experience break us or to rise above it. Perhaps I'm naive and insolated by my skin color and middle-class financial status, but I've always felt that things would have to get really, really bad before I felt like I didn't have any options.