According to Mr. Kan, it almost happened to Airbnb.

Mr. Kan and his co-founder Michael Seibel first met Airbnb founders Brian Chesky and Joe Gebbia after SXSW in 2008. Back then, the online market for renting out your home was touting the sketchier concept of an air mattress on a stranger's floor and had already tried launching at another conference on design in San Francisco. Writes Mr. Kan:

These were guys with very little knowledge of the tech industry, two designers who had a programmer working with them part time. Michael was advising them, and every couple of weeks they would come by the office to talk with him (while the rest of us alternated between watching casually, mildly annoyed that Mike wasn’t working, and actually trying to provide helpful advice). The one thing I remember vividly was the time when they first demoed their payment flow to us. It was built on top of Amazon payments, and was quite frankly atrocious and we told them as much (I think it required multiple redundant fields).

That summer, they launched a third time for the Democratic National Convention and achieved some traffic, which promptly went away soon after the conference was over. By fall, almost anyone could have justified throwing in the towel. They had tried to make the product work multiple times, had accumulated tens of thousands in personal credit card debt, and were literally printing cereal boxes to try to make money. Even their lead (and only) engineer had moved back to Boston. As a casual observer from the outside, they appeared isolated and discouraged.

But they didn’t give up. They kept at it. At the end of the year, they were accepted into YC, and immediately started trying to generate revenue and hit profitability. Two years later, Airbnb has a great product, a huge userbase, great revenue and is the the toast of the town in Silicon Valley. They are even a contender for the most valuable YC company created to date.

Mr. Kan's post is clearly intended to be inspirational, rather than strategic. But aside from its last line, "I can’t promise you will succeed if you stick with your start-up. What I can promise is that if you give up, you won’t possibly succeed," it doesn't address the nagging realization that sticking with a concept doesn't necessarily mean your start-up will provide value, particularly if your concept doesn't suddenly open up "the eBay of spaces." In some cases maybe that flight instinct is trying to tell you something.