If someone is a child of a farmer and hangs out in a tiny farm town without internet access, doesn't complete high-school, their odds of creating great wealth are zilch. They may start a hardware store but don't get your hopes up that they'll be the next Sam Walton. Whatever they hope do, it will be much harder. Some of the doors are closed, some doors don't matter.
If someone where a Ruby developer and wanted to work for a startup, a degree probably wouldn't matter as much as say MegaCorp.
But if someone goes to an exclusive university, graduates and then lives in a large city and has lots of friends, their odds of wealth dramatically improve versus the former... if they were ambitious, many more doors would be open to them (vendors, partners, investors, customers, etc.). Being close to the action with the right contacts is a world of difference from being a random person without successful, helpful friends and pedigree.
Furthermore, it is valid to be self-reinforcing because it is. Without wealth, it's impossible to capitalize on opportunities to make smart investments which one would otherwise have to pass on while others with more wealth may have the chance to make more money on them. Also, people with wealth have plenty of pseudo-"friends" pitching them opportunities to make wealth, whereas someone without wealth is unlikely to have a full calendar of people trying to get investment from them. Think of how many deals Mark Cuban can pass on just because he doesn't like the terms, and how good he's gotten good at negotiating favorable equity terms and knowing which deals are good/bad. Someone that's totally new is likely to be totally inept at some part of the business dance and will likely get rooked. Someone with the right friends is far more likely to get good advice from them about what to do or not do in a business setting to make fewer mistakes.
It's harder to get from zero to having VC's for friends that send you sweetheart deals to invest in, but that usually requires proving oneself (rich) first.
In conclusion, rich does not assure itself but it tends to be self-reinforcing.
(I took the ten-year plan and barely finished because I subconsciously resisted due to the conscious futility of it. Box checked, not about to start Dr. ... PhD)