"Taking a risk for getting richer by having a freedom for doing what you love".
(Freedom) Working for others could be fine if you are key person, because others will listen for you, otherwise you are treated just yet another (hard) worker. You don't have freedom, that's fine in business, they understand their business well.
(Rich) Zuckerberg, Page, Brin, Ellison, Gates, Jobs, Jack Ma, you name it, all of them are founders, sure some others can get richer by joining later, but you should work really really hard in order to be a key person in a well established Corp.
(Risk) You might lose lots of things, not just money and founders love to take a risk, they are driven by adrenaline :)
(Passion) You are going to do things what you love, because that would be yours. when you don't have motivation you don't care and you will work, because that's yours. when you are tired, you take little rest and you will work again, because its yours. In hard days, you will find a way, because that's yours. But when you are working for someone, you don't always feel this, you might quit anytime, but when that's yours you are not going to quit easily ;)