NEW YORK ( TheStreet) -- After a string of disastrous investments and his departure from Yahoo!'s ( YHOO) board last Friday, it's time for Carl Icahn to hang it up running other people's money. Here's why. Icahn's decision to leave the Yahoo! board comes a year after mounting a costly and distracting proxy contest to get elected. That's his right, of course. After all, investors in his Icahn Partners hedge fund were the ones who footed the bill for his efforts. Those same investors -- including Icahn himself -- are also sitting on a loss on their Yahoo! investment. We don't know the exact magnitude of the loss but it appears, based on a review of the SEC filings, to be on the order of -23% or roughly $320 million on 60 million shares held at the end of June. Icahn's stated reasons for stepping down from the board were that he no longer had the time and Yahoo! no longer needed an activist. If he's right, then someone should inform Icahn's buddies John Chapple and Frank Biondi, who came on Yahoo!'s board last year with Icahn. Their whole legitimacy for serving on this board is now in question based on Icahn's comments. They should make like their buddy and head home to Manhattan. And with Yahoo!'s stock at less than $17, far less than Microsoft's ( MSFT) offer of last year, it seems incorrect and premature to declare the company a success and not in need of further changes.