It basically defends that no one comes from nothing and becomes someone all of a sudden, the author says that the people who have become successful in life have taken advantage of opportunities that have been given to them or have not been given. That's all well and good but anyone with little sense should already know that!
So basically a persons success is not earned one way or another but you have to hope for some things to happen to you or opportunities to pop up in front of you to become successful or not, or as the book states are born in a certain time or another...
Part of Bill Gates success was apparently because he attended a school which housed computers before any other school. Well, he could have read in a magazine about computers and searched for a school with computers and attended that.
And if you are not successful it's not because you did not try hard its because you were not lucky enough for some things to happen to you in life... well what's the point of anything happening to you in life then?