I squeezed into a seat in the front row of the press section, just over Mr. Zuckerberg’s right shoulder, and settled in for a marathon session. (You’re not supposed to bring food or drink into these rooms, but I was warned it would be a long session with few breaks, so I smuggled some trail mix in my bag.) My seat was tiny and uncomfortable, with less legroom than your average discount airline. But the hearing itself was fascinating, and I quickly forgot about my discomfort as Mr. Zuckerberg began his testimony with a statement in which he said, “We didn’t take a broad enough view of our responsibility, and that was a big mistake.”

I’ve been covering Facebook for a long time — an embarrassingly long time. In 2006, when I was in college and Facebook was a two-year-old website that was only open to people with .edu email addresses, I wrote a paper for my freshman year English class about why Facebook was going to revolutionize social life at our school. That turned out to be true, but I wasn’t as prescient about Facebook’s future trajectory — I predicted that the social network would never be a huge success because there was no way it would ever let adults join. Oops.

One of the reasons I love writing about Facebook is that it’s less like covering a company, and more like covering a foreign country. There are 2.2 billion people on Facebook, and those people do all kinds of fascinating and terrifying things with the tools Facebook gives them. Mr. Zuckerberg, the authoritarian leader of this “country,” is a compelling character in his own right, and watching him answer Congress’s questions about Facebook’s inner workings was deeply revealing. (If occasionally frustrating — such as when tech-challenged senators asked him basic questions about how computers work, which at times created the sensation of watching a very long Genius Bar appointment.)

My own Facebook feed is a total mess — I wrote a column last year about joining more than 100 Facebook groups, and permanently throwing off Facebook’s idea of who I am as a result. I imagine that the algorithms saw me joining groups like “Flat Earth Believers” and “Quilting For Beginners,” along with lots of pro-Trump and anti-Trump groups, and just gave up on targeting me.

But as I sat in the halls of Congress, watching Mr. Zuckerberg testify in front of dozens of angry lawmakers, I logged on to Facebook, and right at the top of my feed was one of those “10 years ago” memory posts, with a throwback photo from my college years. It was a bracing reminder of how simple and harmless Facebook used to seem, back when I wrote that English paper, and how much has changed since.