Ask HN: When to use or not use your own money to fund your own startup

According to techcrunch, Tony Conrad created a startup called Sphere which was acquired by AOL for an estimated $25 million. Then Tony decided to start about.me but when he did he raised over $400,000. Why didn't he use his own money to fund about.me?

On a more local level. I feel like I have finally saved enough to start my own startup and if I fail I just lose 1/2 of my savings. I don't want to fail and then be in a debt that I can't ever get out of. How does one determine if they should spend their own money on their own project or not?