Understood, but this isn't a founder pointing out that they have chosen this life, this is an investor (by definition has a profit motive) in an educational context (startup school) saying that founders can't be successful and that they shouldn't even try (question was "how do you know if you have what it takes?") unless they sacrifice everything else in their life for the business.
It's the difference between a priest or a nun following what they believe is their life's calling and a televangelist promising their audience blessing if only they'll sacrificially give their life savings as offering.
It's also worth pointing out that Ron Conway (as far as I can tell) was never actually a founder himself. He's not had to take his own advice. To be fair, I'm not familiar with all the details of his life, so maybe I'm mis-characterizing.
I've spent a good portion or my career working with and for startups and small businesses, so I'm not just against them on principle, but this advice, coming from this source really feels off to me in the same way that as a Christian televangelists feel disturbing and off.