[ChuckMcM]

The filter line is typically execution risk, which is to say that once you've demonstrated that people will pay enough money for the product that you can fund the business, growing the company to the point where it is net cash flow positive flips the switch.

The thing about Theranos was, as we found out, that they had yet to prove their fundamental thesis which was that you could do a useful number of diagnostic tests with a small amount of blood to the same confidence levels as the same test done the existing way. Fundamentally they could not show that to be true.

So in a more critical (or perhaps skeptical) investing environment, they should have stalled out several years ago when they couldn't demonstrate to new investors that they had a viable blood diagnostic process[1]. But for what ever reason that didn't happen.

[1] And yes there are stories that they simply lied about what was happening.