I would guess wealthy or powerful connections matter a lot. Ideally if they are family, childhood friends etc. I know that is a sucky answer but I am assuming

I would guess wealthy or powerful connections matter a lot. Ideally if they are family, childhood friends etc. I know that is a sucky answer but I am assuming you mean all billionaires not just the completely self made ones. Also for most people making a few million is enough to solve the money problem. There may not be any further desire to get rich. However if you do have that desire and it outweighs other psychological constraints (avoiding fear, pain, change etc.) and that desire can last decades then it is possible to get from well off to rich.