What was the source of these revelatory, self-image-shifting facts? The same place you probably went when you got to work this morning: Facebook, which we can’t stop feeding, and obsessively tracks our every online movement.

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Over the course of five or six hours on July 17, I pored over my News Feed, endlessly scrolling and refreshing until every piece of content that appeared was a repeat. I cataloged each post, totaling 1,417 status updates, photos, links, Likes, event RSVP’s and more, creating an assortment of everything Facebook thinks I care about.

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But for all those link shares and wall posts, I still wasn’t sure exactly why I was seeing what I was seeing, or if I was even seeing what I wanted to see. (A Pizza Hut co-worker? Really?) So I went through my whole Facebook network – all of my 403 friends and the 157 Pages I Like – and recorded every single thing they posted on July 17.

Spoiler: My News Feed showed me only a fraction of my network’s total activity, most of what it showed me was old, and what I was shown was often jarringly unexpected.

Facebook says roughly one in seven people on the planet log in at least once a month. And yet, how News Feed works remains bafflingly opaque, like a secret box of technology, algorithms and magic that remains one of tech’s bigger mysteries. An entire consulting industry is built around trying to game it (think SEO for Google), and publishers invest enormous amounts of energy into succeeding on it, but as soon as people start to figure it out Facebook tweaks its secret recipe and everything goes out the window.

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What we know is this: The more popular a piece of content posted in your network becomes, the more likely it is to spill into your News Feed; and the friends and Pages you interact most with are the ones you’ll see most frequently, according to Justin Lafferty, editor of InsideFacebook.com.

“Mark Zuckerberg wants News Feed to be like a newspaper,” he said. “The top stories are curated based on relevancy and the user’s connection to that page or friend,” he said, adding that like a printed newspaper or magazine, older stories can still be germane.

But beyond that, not much is known, and the further you dig into what Facebook thinks about you, the more odd things can get.

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For example: I lived in Denver until I was 20 and still consider it home. Throughout my day on Facebook, I didn’t see a single story from The Denver Post, despite that Page posting 17 pieces of unique content. The same was true for Westword, a Denver alt-weekly I used to read religiously; a handful of local TV news stations I Like; and high school friends, acquaintances and even people I still consider close friends who live there. Do I not care about my home as much as I thought? Despite letting Facebook track me basically wherever and whenever it wants to, it still doesn’t think I’m interested in Denver or what goes on there?

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On the other hand, women-oriented blogs such as Jezebel, Refinery29 and The Cut at times dominated my News Feed, with a whopping 40 posts between them appearing. The Verge, which I thought was among my favorite blogs, barely showed up.

And even as I was doing my experiment, I could see subtle shifts in what appeared, which, in turn, perhaps changes who Facebook thinks I am. Status updates from those same high school friends I hadn’t interacted with in years suddenly started popping up toward the end of the day. The same went for Pages I liked long ago and forgot about, and parties in New York I wasn’t invited to but saw close friends RSVP to.

The day had become an oddly pointed reminder of a past I don’t seem to care about, and a distressing collection of everything I’m missing out on today.

By midnight, after almost six hours of scrolling, refreshing and note-taking throughout the day, I had consumed 1,417 unique events. Posts from July 17 became rare as older posts crept in, and eventually everything I was seeing in my News Feed I had seen before. I had exhausted my well of Facebook content, I thought – a triumph! I had conquered Facebook!

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Well, no: I wasn’t even close. After going back to record every single event that happened in my entire network on July 17, I saw that 2,593 pieces of new content had been produced. I saw 738 of them, or about 29%. The other 679 posts that appeared in my News Feed were old news by the time I saw them, sometimes by more than two days.

So that means that after doing everything possible to see all of the activity in my network, I saw less than third of it. Considering the average U.S. user spends around 40 minutes on Facebook per day – or about one-tenth of the time I spent in my News Feed – it’s easy to imagine that percentage dipping far, far below my 29%.

But that might be the point.

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Greg Marra, a product manager on News Feed at Facebook, told me that it is fundamentally a reflection of the user and his or her interests.

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“News Feed is made by you,” Marra said. “It tries to show the most interesting things possible for you, it’s a very personalized system,” he said, adding, “We try to let users take control.”

Marra said there are countless signals that tell Facebook what to pump into a person’s News Feed, including relationships with other users, the topic of content in a given link, how long a user spends reading a story he or she found though Facebook, if and how many times X user visits Y user’s profile, friends’ activity on a certain post, all of our previous activity and more.

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“We learn based on what you’ve done in the past,” Marra said. “And we try to quickly learn about the things that you’re interested in.”

(Remember that Facebook’s learning can sometimes result in disastrous PR.)

So after a full day spent on Facebook, what was I left with? In the end, not much. A heap of work for myself to complete this story; a still-muddled understanding of how News Feed works; and a slightly different view of what I think I care about.

Fittingly enough: The final post I saw on my Endless Day of Facebook was a status update about a flash flood warning that was more than 40 hours old.