This is the point that has really started to become clear to me in recent years, and not just for startups but for artists, authors, athletes, and all the other dream jobs we idolize: so many of these people are either (1) not really making that much money or (2) already had a trust-fund or come from a wealthy background so they can spend all of their time writing, painting, or engineering. Most authors make below the poverty line [1], and Facebook's success was the outlier, not the norm.
I did the start-up thing in my 20s for about 3-4 years (in the 1990s). My income was about the same as my salary would later be when I went to work for another company, but my stress-levels dropped significantly when I started working for someone else. The constant uncertainty was gone, I was watching my savings grow instead of decline, and I do regret not going for that stability sooner.
I see a similarity between tech-kids in their 20s chasing start-up dreams and the poor kids from my old neighborhood chasing hoop-dreams. The tech-kids have better options to fall back on, but the chances of becoming that rockstar million/billionaire CEO/professional athlete are about the same.
[1] http://www.theguardian.com/books/2015/sep/15/income-for-us-a...