Just now I have only two ads on the side of my Facebook feed. One is for organic cotton sheets and the other offers to sell me the “best reviewed” mattress. I am seeing these two ads because yesterday I was shopping for organic sheets and a new mattress. You see the connection, right? Facebook knows where I have been and so do the newspapers I read. Twist ads always appear in the middle of my Times stories. If I look too long at a lamp on the Crate and Barrel website, the company sends me an email warning me how few they have left in stock.

I have the general understanding that cookies are involved. It is as if I were shopping at a mall and someone continuously walked behind me, noting on a little pad of paper what I look at and for how long, and then sent me junk mail based on those notes.

Except that the internet does it with computers and they do it far more efficiently.

Mark Zuckerberg is testifying before Congress this week. Many of those asking him questions seem not to understand how social media works. Despite, an excellent article in the Post, which illustrates how little those questioning him understand social media, I wonder how much most users understand.

The platform exists to make a profit and it does this by selling our shopping habits, also our political and social concerns. It also made money by selling space to propagandists Cambridge Analytica, bent on electing Donald Trump as president.

 “It was my mistake, and I’m sorry,” [Mark Zuckerberg] said.

He sounded as if he had broken a vase, not a democracy.

But the entire purpose of Facebook is to make money by treating its users as the product that it sells to advertisers. Anything that impedes that is going to be extraordinarily unwelcome — and thoroughly resisted — despite Zuckerberg’s insistence to the contrary.

In case you were in any doubt, Facebook makes a great deal of money selling space and users. Is there a difference between selling space in order to convince you to buy “the best reviewed bed in the world” and trying to sell you lies about our political candidates.

Yes, dears, there is a difference. We were sold, and in this case we were sold to people lying to us about our country. And while Zuckerberg is in some trouble just now and has vowed to fix this “problem” (Facebook stock is back up), I assure you that he will continue to sell to whomever is willing to pay.

I knew signing up that Facebook was for sale, and that I was for sale by using it. I weighed benefits (no cost up front) against cost (someone collecting my information) and chose to participate anyway. When I see the lunatic memes, I call them out or let them pass depending on my mood and whimsey. I am not the web police. I am the daughter of parents who believed in getting facts straight. I make my living by teaching others, among other things, to distinguish between opinion, fact, fiction, and outright lies. (They do not always learn.) When the claim is important, I check it out.

Most of what I read on the internet is marvelous and accurate reporting. Some of what is posted on the internet is trash. Even news markets vary. When coal miners were trapped underground in Chili, Fox News had the only reporters who remained until they were rescued alive after their record-length 69 day entombment. But Fox & Friends, the channel’s afternoon “news show” is about as trustworthy as three of your alcoholic neighbors working on their second or third sixpack. They might say anything. A reporter on a morning news show offers a “maybe” conspiracy theory, and by afternoon the Friends are reporting it as fact.

Know your sources, and doubt the outrageous story. If whether it makes you furious or frightened: Check and verify. Avoid the “op-ed” and “opinion” pieces if you want straight news, but be aware that being aware requires trusting the right people.

The truth is out there. It is rarely as entertaining as you might wish. It is always more complicated. Distrust the easy answers. No one is out to get you . . . They just want you to buy their brand of mattress. They want your vote. “Follow the money,” the saying goes.

Your attention is for sale. Beware.