Eerie coincidences aren't that eerie

Is your phone listening to you? I think a fairly consensus suspicion is that it is—that social media apps are picking up your conversations to sell you ads. We suspect this because it’s surprising how often an ad will appear that reflects your recent conversations. You speak about something random—something you’d never normally talk about—and lo and behold within a couple of days you’re shown an ad for said random thing.

I’m not so sure. You know, I’m a pretty paranoid person. I use Graphene OS rather than the Googled Android OS. I have my Instagram in a different profile, so it’s isolated from my normal day-to-day usage. I do a bunch of things that would make this kind of listening impossible, even if it were happening. And still, I’ll notice oddly specific ads that seem absurdly relevant to recent conversations and not much else.

Now, our phones may well be listening. I’m no phone expert. But I’m rarely sure this kind of suspicious coincidence is more than exactly that—coincidence. Let me tell you why.

I’ll start with a completely unrelated example. When I’m marking student essays, I almost always only comment on things that need correcting. Much to my students’ dismay, if what they’ve written is good, I rarely stop to make a note of it. You do this too. Maybe you’re reading a book and you’re completely absorbed, until you hit a typo and you’re suddenly jolted back into yourself.

This is because one of the core jobs of our brain and body is to come alive when it notices interruptions. Our nervous systems developed to map actions to the environment, and they were doing this long before brains were a thing. But it wouldn’t make sense to do this online—every moment of every day, your neural system actively working to connect your perceptions to the best possible responses. Usually, the best possible responses are highly prescribed and the body can manage this passively.

Our environments, on average, aren’t very varied. I mean, they’re often very complex and human behaviour is extraordinary in many ways, but there’s a reason we talk about our routines and our habits. The environment might be very complex, but we’ve spent our whole lives working out the best paths through the environment, and the vast majority of what we do is done on autopilot. We are, frequently, cognitive misers—we encode the best mappings of perception to action, then let that run in the background until something happens that makes us realise we need to update that map.

This is why I won’t make a note when my students are writing good stuff. I’m not interrupted—it’s a coherent argument, and I’m absorbed until some strange sentence, or illogical statement jolts me into action. It’s the same with you and your book—the book is flowing smoothly through your brain, meeting all your expectations about how books should go until you hit a typo, or some event in the book violates your expectations. Then you’re interrupted. You wake up and pay attention in a different way.

So what does all this have to do with my phone listening to me (or not, as the case may be)? Well, this interruptive feature of the brain tells us something. If the world is aligned with our expectations about the world, then we don’t really do any additional processing. When things are expected, we just glide right past them. We only really notice when things interrupt us. Let me give you one more example, which will bring us back to the point.

Have you ever noticed that buttered toast, if you drop it, almost always falls butter side down? Well, it actually doesn’t. Mythbusters tested this about 20 years ago and found that in most circumstances it’s actually just as likely to fall butter side up. The reason people think otherwise is because we only notice when the toast falls butter side down. If it falls butter side up, you put it back on your plate and forget the incident happened at all.

I suspect this is more-or-less what’s happening with your phone. It’s inundating you with ads, all day, every day. You never notice when the ads are random and unrelated to conversations you’ve had recently. You only notice the odd random ad that is related. The proportion of unrelated to related random ads is probably very very tiny.¹

Probably, most unusual coincidences are this. Simply a matter of not having the counterfactuals to hand to compare the relative likelihood. You never notice all the times the weird thing could have happened, but didn’t. It does makes the world a little less interesting though, so I’ll forgive you for pretending not to notice this article too.