If your startup isn't a labor of love or you're not driven by a strong dislike of an alternative career path, then almost every startup would die the second the founder(s) do the math of income opportunity cost of trying vs stable employment.

Hardly. People do "risk vs reward" assessments all the time.

Balancing "use some savings to live off ramen for two years" vs "implement something people will pay for" might not be very difficult, depending on their existing rate of savings, income, state of mortgage, monthly expenses, etc.