Love the underpants gnomes reference and I agree that many startups will fail. But wow, working at a company you feel in your bones will fail seems to me to be a poor way to spend a career.
Not that every company I've worked at succeeded, but I hoped that every startup I joined as an employee would.
Now, as a contractor or consulting company, you still want the client to succeed, but it's much easier to be arms-length, take orders, and collect your check.
That most startups are Underpants Gnomes, the company probably won't succeed even if they ship.
Even if the company is not Underpants Gnomes and their fundamentals are sound, succeeding or not is still largely luck based.
Maybe the reference to Underpants Gnomes is too dated now? - https://youtu.be/a5ih_TQWqCA