If you want to avoid failure, it would seem like the most important thing is to quit your day job. Most founders of failed startups don't quit their day jobs, and most founders of successful ones do.
These documents were originally created for YC-funded startups to use when raising angel rounds. They seem to have worked well in trial runs so far, so YC is open-sourcing them.
The key to making a site builder for end-users is to make software that lets people with no design ability produce things that look good -- or at least professional.