Nouriel Roubini used to be the man who could swing the markets by 10% with a single comment. No more. Greenlight Capital’s David Einhorncouldn’t move the entire market by 10%, but he sure can move the stock price of a $3.3 Billion company by 10%. Last week Insider Monkey interviewed David Einhorn about his book, Fooling Some of the People All of the Time. The second most important question of the interview was his favorite stock for 2011 (See the most important question we asked here). David Einhorn’s favorite long pick for 2011 is a Dutch insurer called Delta Lloyd. “That’s probably the only stock we have that I think can double and it would still be cheap,” said Einhorn. Insider Monkey is a new finance blog so we were quite excited to learn of David Einhorn’s extremely bullish views about this obscure Dutch stock. Our article was picked by several Dutch websites within a couple of hours and Delta Lloyd stock started its climb. The first day (Jan 4th 2011) it went up by 3.2%, followed by a 4.8% increase the second day, and 2.5% increase the third day. In three days the stock gained more than 10% and has been trading around those levels since. David Einhorn’s endorsement increased the market value of this stock by more than $325 Million. Bruce Berkowitz was talking about sending Einhorn a box of chocolate after his presentation about St. Joe (JOE). We think Aviva, which owns 57.6% of Delta Lloyd, and other investors of the company should take note. David Einhorn’s Greenlight Capital owns between 5% and 10% of the Dutch insurer, so Greenlight had more than $17 million of paper profits in three days. David Einhorn isn’t 50 Cent. This isn’t a pump and dump scheme in a penny stock.It's public knowledge that David Einhorn owns at least 5 percent of Delta Lloyd, according to a filing made on May 7^th, 2010 in the Netherlands. Last year he shared this information with investors in one of his investor letters as well. Investors have two things to learn from this story. First, they should follow David Einhorn’s comments because it can affect stock prices and they may be able to make money by monkeying him. Second, the Efficient Market Hypothesis is a HUGE lie. It took Delta Lloyd stock three days to digest Einhorn’s endorsement. It is not true that “markets are so efficient that they instantaneously reflect new information”.