You can start making money with less than a good product. And needing no customer feedback, because you have long runway, may actually not be the best external stimulus to choose.
(Take this opinion with a grain of salt, I haven't done my own startup, yet.)
Andrew Mason first had the idea for Groupon in September 2006, which was more than 2 years before Groupon officially "started" in November 2008, and probably at least 3 years before they achieved mainstream success.
That's the sort of iteration that basically every business needs to go through, though. The great-grandparent post points out Groupon as an example of a business that succeeded in much less than 2-3 years because it started with a business model, and I pointed out that Groupon neither had a business model when it started nor took only six months. This whole subthread started with a question about whether 6 months is adequate for someone just now quitting their day job - it's most likely that someone in that situation is at that "I'm thinking of a web platform for collective action" stage, not at the "I have a web platform for collective buying" stage.
My mom first had the idea for rollerblades in 1968 — that doesn't mean she's a cofounder of Nordica. Thinking of an idea for a business is so many light years away from actually acting on that idea.
It sounds like Mason was actively working on The Point/Groupon for those two years, not just passively thinking about it. He quit his day job in 2006, he was enrolled as a student during the time period, he launched The Point about a year afterwards, he was in full contact with Lefkofsky during the time, and he launched Groupon a little less than a year after the decision to refocus The Point on something that could actually make money.
That's very different from dreaming up an idea and then forgetting about it for 30 years while you work on your day job.
http://friendfeed.com/paul/0268007b/how-long-does-it-take-to...