Current Yahoo CEO Marissa Mayer could use an extra $54 billion. AP Photo Here's a painful reminder for Yahoo shareholders.

In 2012, then-CEO Scott Thompson agreed to sell 20% of Yahoo's stake in Alibaba. At the time, Alibaba was a private company with a ~$30 billion valuation.

Today, Alibaba is a public company valued at ~$300 billion.

Yahoo shareholder Eric Jackson says that Thompson's decision to sell cost Yahoo $54 billion.

To put that number in perspective, Yahoo's market valuation right now is $48 billion.

There is some additional context to consider here. Once Yahoo agreed to this deal, it set Alibaba's initial public offering in motion, which led to its $300 billion public market valuation.

Further, at the time Thompson was on the outs with investors, so he needed to do something to save the company. Investors were also getting antsy about Yahoo's stake in Alibaba. They wanted Yahoo to dump the shares pronto to get the cash.

At the time, selling Alibaba shares wasn't universally regarded as a massive error.

Now, it should be.



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