Visionary Perseverance vs Stubborn Stupidity

A few days ago, I heard a talk by RE-Power’s CFO. He took us through the company’s quite incredible journey. In early 2005, the company was a cash strapped sub ~€70m market-cap company, and no investor was willing to put any money in it. But by 2008, the stock price had gone up ten fold and the company was worth a couple of billion euros.
One of the conclusions of the speech was that if you believe in what you are doing, you should persevere, and you will be successful.
One hears this conclusion quite often in the retelling of success stories. But the problem is that when you hear about stories of failure - and normally such stories do not make it to a key note address – it is told by the investors who were smart enough not to invest. “Every one told the CEO it was a stupid idea, and he just went on wasting his time on it. It was clear it was going to fail.”
It seems that the line separating “stubborn stupidity” from “visionary perseverance” can only be drawn in retrospect.