I have asked myself this question many times, and the best answer I have been able to come up with is
1. Somebody has to be on top, we can't all be equally rich/attractive/intelligent
2. It doesn't really matter. Think of it using this analogy. Life is a marathon, but we don't all have the same starting line. Some of us start a little farther up, and some of us start farther back, but nobody is really more than a mile from real starting line.
Now somebody who has everything going for them, born with all the right genes, born into a loving, nurturing and wealthy family, and born in and industrialized nation with good education and health care. That guy who was dealt the perfect hand starts out a full mile ahead of the staring line.
Now on the other end of the spectrum you have someone who wasn't handed everything on a silver platter, he isn't as smart, he is born in a third world country, and let's say he lives in an orphanage. It doesn't get much worse than that, so he would be like a guy starting a mile behind the starting line.
Now we have these two racers they are a full two miles apart, can't even see each other, but they both have the same finish line, the same goal that they are working towards. Who is gonna win? Odds are the guy in front, yes, that is true, but the guy in the back has a chance, a very good chance, especially if he is willing to try just a little harder than Mr silver spoon.
The point is that all the advantages or disadvantages in the world pale in comparison to the power of human spirit. And someone with dedication and drive will always be more successful than someone without those qualities, regardless of the starting point.
Maybe that analogy is kinda weird to you, but it makes sense to me and that is how I rationalize it.