Perhaps the most surprising sentence in Twitter's IPO documents Thursday — and the most troubling news for fans of the social media service — came on page 23 of its S-1 filing.

"We have incurred significant operating losses in the past," the company said, "and we may not be able to achieve or subsequently maintain profitability."

Translation: Twitter hasn't made a dime. And there's no guarantee it will in the future.

The company lost $67 million in the first half of 2013, the filing revealed, and it has an accumulated deficit of $418.6 million. That total shortfall is larger than its revenue last year, $316 million, itself a smaller number than most analysts were expecting.

The widespread assumption when Twitter announced it was going to go public was that it was making something on the order of $600 to $800 million a year. It ain't there yet: 2013 revenue should be around $500 million.

It's encouraging that the first six months of 2013 saw twice the revenue numbers of the first half of 2012. But the losses are increasing too; the company had an $80 million shortfall in 2012, and is probably hitting that amount of loss in 2013 — well, right about now.

It's All About the Acquisitions

So what's going on? Investment, of course. Twitter is hiring rapidly, expanding its offices, and most expensively, snapping up companies. For instance, its acquisition of the social TV service Bluefin back in February? That cost $67.3 million.

Twitter would have been in the black this year to date without that one purchase, to the tune of $300,000. And if it hadn't paid $38.2 million for coding company Crashlytics in January, its profits would have looked even healthier.

But of course Twitter gets a ton of value out of each acquisition, and the price is lower when the company is younger (Crashlytics was a mere year old). We're not saying Twitter shouldn't have bought them; just that the spending spree CEO Dick Costolo has been on is obscuring its profit potential for the moment.

The encouraging news for investors is how much of Twitter's ad revenue comes from mobile users, which is where the real growth potential is. Some 65% of income is derived from Twitter users checking their smartphones and tablets. For Facebook, that number is a mere 41% (and was virtually zero at the time of its IPO).

So yes, this isn't the healthiest balance sheet to be heading into a public sale with. Essentially, Costolo is saying: trust me. This ship is headed for treasure. It has already found some, but it is also taking on a lot of new crewmates. Fund the expedition some more, and we'll discover doubloons beyond your dreams.

Image: Mashable, Christina Ascani