Of course that's true as an outside investor working under the efficient markets hypothesis, which is hard to beat. But it's not how a principal like Zuckerberg, who can actually affect the valuation through strategy and recruiting, should view or portray things.

And I'm not making an extrapolative prediction of Facebook's value, just reminding people that the idea of Apple as a $300B-plus behemoth is itself fairly recent, and required an at-the-time unforeseeable surge in value from its Facebook-like $70B valuation just 5 years ago.

Thus rather than Apple providing an example of a height Facebook can't reach, as the great-grandparent post seems to imply, Apple suggests the opposite, that a $70B company can become a $330B company, in less time than pure faith in the market valuations might suggest.

Finally, the $70B valuation is not a market prediction that the actual trading value of Facebook will remain $70B in the future: merely that $70B is the best consensus average from public information, weighted over all considered futures. Very roughly, maybe there's a 4/5 chance Facebook falls back to $10B, and a 1/5 chance it races forward to $310B. Voila, that risk-neutral average value is $70B. So, a Facebook of Apple's size is 'thinkable', and there's essentially no chance that $70B is its actual value after this all plays out.