Anybody starting a major project will be ignorant about some important things. It's impossible to do anything interesting and know everything up front; if you could know everything, then that would mean it had been done a zillion times before and therefore not be interesting.
There's also a strong selection bias. The kinds of people who don't take chances? They don't become entrepreneurs. They don't bet years of their lives on projects in hit-driven industries. Those who do take chances already know that so many of the things that previously seemed impossible or dangerous to them worked out to be fine.
So nobody should ever, ever, ever not start something because they don't know everything. The trick to successful entrepreneurship is to test your big risks early, so that your failures are small and recoverable, rather than late and fatal. Here their mistake wasn't underestimating the impact of 3D. It was in not testing their assumption before the public launch of the Kickstarter.