No...? What makes you think Facebook is a success Zuck can just repeat at will? Having been lucky once already does not make him a better entrepreneur; though the brand will surely help promoting his new startup, and a billionaire has certain connections mere mortals don't have. But neither of those fact are tied to him being a good entrepreneur... look at Bill Nguyen to see where this line of thinking leads you. Color is doing great, isn't it?

Don't focus on Zuckerberg. If you think Facebook was just luck, pick someone who you think succeeded by skill. Would you invest in their next company at a $20M valuation?

You've identified by omission precisely why it can be "wrong" for something to be priced "high". How on earth can I know if $20M is reasonable without knowing what the business is?

We're all sat here, reading about "average seed round valuations" and the like, but that concept tells you nothing about what the next startup you meet "should" be valued at. Claiming that it does means acknowledging that business fundamentals have been thrown out of the window, and what are you left with then? Gambling.

Of course early stage startups aren't judged by business fundamentals.

Your argument is fully general against valuing equity in any early stage business ever at any price. It equally says that the investors are "gambling" and the founders are "gambling", as much as anything about employees.

Yes, everyone who is being paid in equity is taking a risk. It is possible to attempt to assess that risk. The key to being an early employee is bringing an investor mindset to the table: do I think this company is going to be successful or not?

Hell no. Zuckerberg has several billion dollars in the bank. He could buy several countries. He doesn't need my money, so he's got to have an ulterior motive if he's seeking outside funding.