It seems to be a long-held belief that Facebook listens to our conversations.

I have spoken to dozens of people who are genuinely convinced that Facebook (or sometimes Google but usually Facebook) is listening in on their calls, identifying the content of their conversation and selling the information to the highest bidder.

You have probably heard something like the following claim many times:

I was talking on the phone to my sister about nappies and now I see nappies ads every time I log onto Facebook. It's like someone has spied on me or something.

First and foremost if, like most people, you think Facebook would actually do such a thing as listening to your private conversations, that says more about their reputation than anything else. And indeed Facebook is a remarkably dishonest, corrupt and overall untrustworthy organization but this is likely not what is happening here.

What is happening has a much simpler explanation and is about how your mind and advertising work.

You see what you want to see

Let's start with your mind.

Have you ever noticed that the number of pregnant women seems to increase when pregnancy is part of your life? (you're pregnant, one of your best friends is, etc)? Or that everyone seems to drive the same car you just drove for a test-drive?

No, you're not going crazy. It's called confirmation bias and it's something scientists discovered over 50 years ago.

Our minds are exposed to a staggering amount of inputs from the external world: images, sounds, names, words, feelings, smells. An incessant and mind-boggling flow of data that your brain has to process every second you're awake. You might think that your brain analyses every single bit of data it receives but that would be naive. Instead, your brain takes "shortcuts" that help it process all this data in a more... efficient way.

One of this shortcuts is, in fact, the confirmation bias. It works like this: your brain will search for, interpret, favor, and recall information in a way that confirms your preexisting beliefs. In other words, you are much more likely to notice something that matches your view of the world.

What does this have to do with Facebook showing me nappies?

Well, Facebook has probably been showing you nappies for months but you simply didn't notice until you had that conversation with your sister. But after you had that conversation, maybe one that was loaded with emotional meaning (talking about the sacrifices and rewards of motherhood), you will notice EVERY SINGLE ad about nappies and will start to believe you've been targeted.

Bear in mind that you probably see dozens, if not hundreds, of ads on Facebook every single day but can probably recall only a handful of them.

Which ones? The ones your brain has been "trained" to see. The ads that talk about things that are "important" in your life or have happened very recently.

You have got this the other way around. Facebook has not started to show you nappies (or beer making machines or ping pong tables) because it listens to your conversations. You have finally started paying attention to these specific ads.

Understanding Facebook's Audiences

You might think: "Ok, I get that, but why was Facebook showing me nappies in the first place?"

To answer this question, you need to understand how digital advertising (and especially Facebook ads) works.

Facebook advertisers can choose between a myriad of options for the target of their campaigns. These options include demographic data like gender, age, race and religious orientation, and also behavioural data like who is getting married soon or who is a frequent flyer. Facebook is without discussion the most sophisticated machine for people profiling the world has ever seen.

But here's the thing: most advertisers, especially the less sophisticated ones (and since Facebook's advertising platform is self-service there are A LOT of those), don't use the advanced behavioural options and rely mostly on the demographic ones.

So if you're a western man in his late twenties/early thirties you'll likely be targeted for tech gadgets, cars and suits. Likewise, if you're a western woman in the same age group you will be targeted by a lot of advertising about baby products, wedding gifts, house furniture and nappies... all things that you are very likely to talk about in a call anyway.

On top of this, Facebook actually makes people see the same ad over and over again because they know repetition increases familiarity which in turn leads to trust. You might not even consciously notice it but you probably see the same ad up to 20 times before Facebook stops it.

Sorry to break the news: in the eyes of advertisers we are all extremely predictable.

You should delete Facebook anyway

The "mystery" is then explained: out of the hundreds of ads that are targeted at your demographic group you actually only remember a few and ignore the rest. These few ads you remember are not random but are about the things your mind considers "important" in that specific point of your life. Finally, Facebook's Ad algorithm is designed to make you see the same ad over and over again.

So, no Facebook is (probably) not listening to your conversations but that's not meant to be reassuring. They are not listening to your conversations because they don't need to. Facebook knows so much about you that can make you believe they're listening to your personal conversations.

And THAT is the really scary thing.