He also has concerns about significant selling holders in the IPO, including management.

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That was the highest proportion in any year since at least 2004, according to Renaissance Capital, an IPO research and investment-management firm.

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Management had delayed an earlier IPO that had been expected last fall.

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Hansen is a major investor in Facebook with 36.3 million shares owned through his firm, Valiant Capital Management, at the time of the IPO filing.

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Typically, insiders (management and venture capitalists) hold back on selling shares in the IPO and instead opt for standard lock-up periods.

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Mr. Grimes himself told the Facebook management team that it would be "his throat to choke" if the IPO turned out to be unsuccessful.

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