I wasn't sure what he meant by premortem. I listed before the 3 plausible things that could go wrong, and he said that that wasn't a premortem, so I figured he was thinking more along the lines of "think of anything and everything that can go wrong".
To your points...
lack of buy-in to the website (just because the people you asked say they would be interested doesn't mean that people will actually use your website; the overall user experience is pretty crucial to determining that)
I'm highly confident that this will be something people want. I have a strong intuitive belief in this, and I actually have talked to lots (hundreds?) of people who say that this is something they do/would want. Still though, I should have mentioned this as a risk.
failure to convert a user base into revenue flow
I don't see this as a problem. If I my website becomes the go-to place for college applicants (or at least one of the go-to places), it'll get a lot of traffic, and the traffic will allow advertisers to target a particular audience (college applicants). From what I understand, on the web, traffic pays.
lack of perceived legitimacy of the reviews (e.g. due to the small number of responses per question), possibly caused by push-back from more established places like the U.S. News & World Report rankings
That's definitely a worry, and is one of the main things I want to address. Once I get rolling and get resources, I want to invest heavily into getting the most reliable information as possible. Still though, all the other student review websites have the same issue of perceived legitimacy, and they've been around getting users for years.
people who say that this is something they do/would want
Why aren't these people using the sites that already exist? You could just say "that's because the questions/answers aren't good enough," but my guess is most of these people who say they would want it never got as far as looking at these other sites in order to see their quality of questions and answers.
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?