I think it's important to be flexible though. If an idea does not seem to be getting much traction, you might consider moving on to your next idea.
For example, with Google, Google AdSense was the glue that made everything work (profitability, great product, many users, good reputation, ability to have free food.) You might say their demo and pagerank was actually important, but they couldn't even sell that for $1 million dollars. Heck, even right now, nobody would buy their original technology as Yahoo! and MSN must have already surpassed the original PageRank in quality.
Of course, if you are trying to keep your idea secret, then this could be difficult to do.
That's when it hurts.