Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: It appeared that investors at Fabrinet (NYSE: FN) couldn't get to the exits fast enough today as shares plummeted as much as 26%.

So what: Today was the scheduled date for Fabrinet's secondary offering to close. Through the offering, insiders signed up to sell 7.2 million shares, a tally that was upsized from the original 6.9 million. There's nothing like a huge chunk of insider selling and 20%-plus of your outstanding share count hitting the market all at once to put pressure on your stock.

Now what: The primary seller in this offering is Asia Pacific Growth Fund, which previously owned 45% of the company. This is a private equity fund under H&Q Asia Pacific, and it shouldn't surprise anyone that they're selling. The Fabrinet IPO has been a big success, and private equity firms aren't generally in the business of holding lots of stock in publicly traded companies. Instead, they want to cash out the win, show their investors the nice return, and focus on other investments.

But while the selling may be very explainable, it still doesn't help the fact that this is a low-volume stock, and there are a lot of shares the market will have to absorb. On the upside, investors that have had their eye on Fabrinet may find that the selling pressure is creating a good buying opportunity.

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Fool contributor Matt Koppenheffer does not own shares of any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool's disclosure policy prefers dividends over a sharp stick in the eye.