Isn't that the point of those companies though, that you aren't seeing traction for a while? It could be that PG is making the distinction implicitly between revenue/profit and traction.
So for example twitter, FB etc... were not profitable or getting revenue well after they had already amassed millions of users. If that is the case, then we aren't learning anything new and it doesn't help people who are trying to make new, hard, breakthrough technologies.
As in, the more traction you show, the harder it becomes to continue that traction, or alternatively, more traction is now expected of you. Combine this with the increasing complexity of a growing machine.
Maybe PG's analogy is that at first it starts off a pinch, but grows to be a very large guillotine until you finally can outrun it.
Absent other advantages, you will need to get to product-market fit pretty quickly if you want to survive.