I like to think of business success in light of one of my favorite quotes:

"Luck is what happens when preparation meets opportunity." - Seneca

Scott Adams' book "How to Fail at Almost Everything and Still Win Big" also touches on this, suggesting that skill + hard work don't automatically result in success (there certainly are factors beyond our control), but it's a lottery that you can keep playing over and over with no real inherent cost other than time. Especially in software, you can test a lot of ideas with very little financial risk/investment, and persistence often allows preparation and opportunity to meet. There are no guarantees of course, except the guarantee of failure without trying.

A lot also comes down to your definition of success. I'd say aim high, but expect very little. Expect the kind of return you'd get from a hypothetical full-spectrum new venture ETF. A handful of unicorn successes averaged with a huge tail of losses = returns that are probably really depressing. Be happy with anything above that.