But that's the point - 2/3 of what you'd get from an established company, multiplied by a few years, is a very large amount of money.
If "maybe 1/3rd of what I’d get from an established company" was enough to pay mortgage and provide for a family of 3, then in the "not doing a startup" scenario you'd have earned&saved that money, and you effectively lose it if your startup doesn't work out.
Sure, but it’s not like I was living under a bridge or anything. My standard of living did not change one iota. The stereotype of a starving founder is just not true most of the time. In fact I’ve yet to meet a founder who did not pay him/herself a pretty good upper middle class living wage. Not millions, natch, but still six figures.
The point is not about living under a bridge or starving, the point is that this should be considered equivalent in most terms (except tax-wise) to earning your market-rate salary and choosing to invest 2/3 of that cash into the startup.
No matter how much you have left, the consideration of whether it's a good deal or not should include that choice to "spend" that amount of (potential) money on the startup versus whatever you would have done with that money otherwise. If you wouldn't have done anything, then there's choice of spending a few years on the startup versus having, say, half a million of savings for retirement.
It was maybe 1/3rd of what I’d get from an established company, but still enough to pay mortgage and provide for a family of 3.
Where do you think that seed capital goes? To pay the founders and whoever they manage to hire.