Harvard, unlike some other Ivies such as Columbia, let's you take time off your degree without penalty to explore ventures and other ideas. So the ones who don't succeed may have simply returned to Harvard to complete their degrees. It is a multiclass, not binary, classification problem.

Makes sense. I am, and I'm sure many other people are too, guilty of modifying how risky and brave a story is afterwards. E.g. "I turned down these job offers to risk it all for this one venture" when in reality the other job offers would have waited a few weeks while you build options. I suspect telling yourself these kinds of stories probably helps boost your own confidence too.

Exactly. It's risk free.

If you become successful people will use it as bragging rights. Otherwise you go back and finish the degree and no one hears about it.

That's an interesting question but it is possible that the number of companies that succeed from Harvard dropouts is actually higher than those of the companies from some unknown University dropouts. People don't usually get that a Harvard dropout has way different (and I mean way better) socioeconomic, cultural and intellectual circumstances to succeed than say some dropout from a below average University somewhere in the world.

Makes sense. If you're a moderately successful individual to go to Harvard, then if you make a decision to drop out to improve your circumstances then it's probably for a good reason, e.g. a good business venture. Similarly that's why we always hear the statistic about those who hop jobs often are the ones with the highest salaries. Whereas if you're less successful and go to a bad school or something, dropping out may also lead to a better life than your current situation, but the bar is a lot lower of what constitutes "better". Also, generally speaking, students in Harvard are probably more career-driven than the average person, so when they drop out they've probably given it more thought than others on average and thus are more likely to make a success of it.

I don't have any statistics, but I had several friends in high school who got into college and ended up dropping out. I don't think any of them regret it. Only one of them dropped out to start his own company. None of them went to Harvard or MIT.

This doesn't mean that college is a bad decision. It's probably the right decision for most people.