One of Yahoo!'s (NASDAQ:YHOO) largest stakeholders is retreating.

Carl Icahn has sold shares of the struggling online giant in each of the past three trading days, enough to take his stake below 5%.

Icahn is typically referred to as a "billionaire activist investor," and he approached Yahoo! last year with the same saber-rattling resolve.

He was initially intrigued by Microsoft's (NASDAQ:MSFT) botched buyout bid, and he established a 50 million-share stake in Yahoo! when it was priced in the mid-$20s. He figured he could slap on some Cupid wings and get the two companies to rekindle their buyout sweet talk. Icahn wanted at least $34.375 a share for Yahoo!, a greedy request when Microsoft had withdrawn its original $31-per-share offer.

His quiver was dry of arrows: Microsoft really meant it when it broke things off.

Yet instead of admitting defeat, Icahn was enraged. Unfortunately, he has found himself rooting for other losing ideas along the way.

Icahn doesn't always get it right. For every BEA Systems that he gets right -- Oracle (NASDAQ:ORCL) bought BEA -- there's a Blockbuster (NYSE:BBI), Motorola (NYSE:MOT), or Yahoo! that goes the wrong way.

You don't have to hit it out of the park every time: The occasional homer will offset a handful of strikeouts. However, sometimes it just doesn't pay to be an activist. There's nothing wrong with "billionaire passive investor" as a tagline.

The world according to Yahoo!:

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Longtime Fool contributor Rick Munarriz will concede that he originally thought Icahn was right on Blockbuster. We're all mortal. Rick owns no shares in any of the stocks in this story and is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.