The better Fitbit's financial performance, it seems, the more skeptical investors get that the company won't be able to keep it up.

The maker of fitness and health trackers reported its first-quarter earnings on Wednesday, and investors immediately slammed its shares for a second-quarter earnings forecast that wasn't as bullish as analysts had been predicting. This even though the earnings report was full of the kind of news investors are usually grateful to hear: Revenue for the quarter surged 50 percent to $505.4 million, earnings per share of 10 cents came in well above analysts' predictions and the company upped its guidance on 2016 profits.

Balance-sheet math aside, the first quarter offered even more encouraging omens, which CEO James Park sought to emphasize on a call with analysts and press. Sales of the Blaze smartwatch and Alta tracker, both introduced in the quarter, accounted for almost 50 percent of the company's revenues. Park noted that the company has sold more than 1 million Blaze units at $199 apiece "despite many casual observers' skepticism."

Indeed, large swaths of the tech press prematurely judged the watch as a bust when the company unveiled it at CES, and Fitbit shares took a corresponding hit. But those who pronounced the Blaze a poor man's Apple Watch got it wrong, with Fitbit now controlling 61 percent of the wearables market versus a mere 7 percent for Apple, according to one recent report.

What the naysayers failed to reckon with, Park suggested, is the role Fitbit's social layer plays in keeping current Fitbit customers loyal and bringing in new ones. According to Fitbit's market research he cited, 44 percent of consumers say a friend or family member "positively influenced their decision to purchase a fitness tracker."

A sizable chunk of Blaze and Alta buyers, 40 percent, previously owned another Fitbit device, an important indication that Apple isn't the only consumer electronics maker with a dedicated following. Moreover, 20 percent of those Blaze and Alta buyers were people who were reactivating their Fitbit accounts after more than 90 days of inactivity. That cuts sharply against the popular narrative that fitness trackers are something you buy once, wear for a few weeks and then leave in your sock drawer.

Those repeat customers didn't come free, however. Fitbit supported the Blaze and Alta launches by more than doubling its sales and marketing budget, to $107 million, resulting in the lower margins that gave Wall Street such pause. But if Fitbit can continue to fend off Apple and convert users to its higher-priced and fuller-featured devices, at some point, Wall Street will have to cool it with the skepticism.

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