Given all of this, I think that if you're smart and hard working, you should have at least an 80-90% chance at succeeding at a startup.
Uhm, I don't think you're multiplying together the likelihood that you don't fail in each of the ways you outlined. You got so close by identifying all the hurdles you have to go through - and then instead of doing the math, you basically said "these look like stuff that can get overcome by a smart and hard working individual" and slapped the "80-90%" label on it.
I counted 21 distinct ways you said a startup can fail. 0.99^21 = 0.8. I'm pretty confident you envisioned more than one person failing in that way out of a hundred.
Interestingly, if you assume these are the only ways a startup can fail, and that for a typical startup creator (who is self-selected as smarter and more conscientious than average) each of these has an independent 90% chance of working out (what seemed to me like a reasonable estimate), then the overall chance of the startup succeeding is 0.9^21=0.11, remarkably close to the actual base rate. This particular model is unlikely to be accurate, but it is another way of illustrating your point.
My motivation behind this post stems from Aumann's agreement theorem. It seems that my opinions on startups differ from most of the rationality community, so I want to share my thoughts, and hear your thoughts, so we could reach a better conclusion.
I think that if you're smart and hard working, there's a pretty good chance that you achieve financial independence within a decade of the beginning of your journey to start a startup. And that's my conservative estimate.
"Achieve financial independence" only scratches the surface of the benefits of succeeding with a startup. If you're an altruist, you'll get to help a lot of other people too. And making millions of dollars will also allow you the leverage you need to make riskier investments with much higher expected values, allowing you to grow your money quickly so you could do more good.
A lot of this is predicated on my belief that you have a good chance at succeeding if you're smart and hardworking, so let me explain why I think this.
Along the lines of reductionism, "success with a startup" is an outcome (I guess we could define success as a $5-10M exit in under 10 years). And outcomes consist of their components. My argument consists of breaking the main outcome into it's components, and then arguing that the components are all likely enough for the main outcome to be likely.
I think that the 4 components are:
The Idea
Your idea has to be for a product or service (I'll just say product to keep things simple) that creates demand, and can be met profitably. In other words, make something people want (this article spells it out pretty well).
What could go wrong?