I agree with VAuroch that this won't help much, because in general taking the inside view is a bad idea.
But if you want a few examples of places you've gone wrong - both getting a good idea, and executing a business, any business, are much harder than you imagine. For example, you wrote:
"Failure to think specifically about benefits." "The big issue here is the first bullet point. As spelled out by Eliezer's article, people are horrible at thinking specifically about the benefits that their idea will bring customers. They're horrible at moving down the ladder of abstraction. They think more along the lines of "we connect people" instead of "we let you talk to your friends". Even YC applicants (probably the best startup accelerator in the world) suffer from this problem immensely. I think that this problem is the single biggest cause of failure for startups. (They say that 90% of startups fail? Well >99% of people can't think concretely.) However, I think that it's something that could be avoided with willpower, reading the LessWrong sequences, and taking some time to practice your new habit."
Well, not thinking specifically is one issue, sure.
But the other, MUCH BIGGER issue, is that you might not know what people want. If you're building something for consumers, there's a problem in that most people don't know what they themselves want (imagine describing Facebook to someone years before it existed).
If you're selling to businesses, then you have to actually understand the business and the market. And understanding markets is incredibly difficult. That's not to say it can't be done, but it's hard even in the best case.
Remember - Some people fail at startups built to serve an industry, after working for 30 years in that industry. They still don't manage to create a product that's good enough.
As for the idea that just executing a business is so easy:
Let's say you decided to build a restaurant. You know exactly, specifically what people want, so there's no problem with finding a good idea, and you know how restaurants work. Talk to 10 restaurant owners and you'll even have a much better understanding. Hell, you're building a business that's been done millions of times before. This is the polar opposite of a startup in terms of "idea risk".
And yet, restaurants fail ALL THE TIME. Because the execution of any business is hard. Hiring is hard. Understanding your market, TRULY understanding it, is hard and takes years of experience. Understanding how to hire and manage people is hard. The thousands of little things you do every day, are all amazingly hard. Each one takes time, each one takes experience.
But the other, MUCH BIGGER issue, is that you might not know what people want. If you're building something for consumers, there's a problem in that most people don't know what they themselves want (imagine describing Facebook to someone years before it existed).
Yes, it's very difficult to predict what people want and will actually use, especially for a solo person. Asking your friends isn't enough because they will just try to make you feel good.
To underscore your point, and try to help us calibrate risks, let's examine the risks of significantly small...
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?