Here's the conundrum. Brands spend millions on above-the-line campaigns, but the most common way for people to share content that may arise from those campaigns is on "dark" social.
I say "dark" in quotes because it's an awful term. Since it is well known it's worth using so we have a common reference, but what on earth is "dark" about people messaging friends privately, rather than posting something for all to see?
It leaves brands vying for attention through heavy spending campaigns, on the one hand, with consumers sharing content behind the so-called "privacy" of "dark" social.
To put this in context, the latest research from GlobalWebIndex and We Are Social shows that two-thirds of consumers, or 63%, choose private messaging to share content with friends.
Rather than post on a public-facing service, the majority are opting for, in order of popularity, Messenger, WhatsApp and the messaging services offered by Instagram and Snapchat.
Entertainment and music content is the top category, following by gaming, clothes and electronic gadgets.
This puts consumer behaviour on an opposite path to where the social giants would like it to be. Open sharing is good for constantly refreshing pages and opening up new opportunities for targeted ads.
It's clear now why Facebook has been prepared to get into trouble over collating data about its customers across Facebook, Messenger and Instagram.
The company promised not to do this as part of getting permission to take over WhatsApp. However, when it broke that promise, a GBP94m fine from the EU must have seemed like a price it was willing to pay for such rich data reserves.
However, since then, we have had GDPR and a large French fine for Google. We've also had the less-reported warning from the German competition authorities that Facebook has a year to stop collating user information across its three main platforms.
The advice, from experts that GlobalWebIndex talked to in relation to the research, was that brands should that accept a lot of sharing is happening where it cannot -- and should not -- be traced.
So the best solution is to have plenty of easily shareable content available to make sure big above-the-line campaigns get traction on dark social, even if it cannot be tracked.
That's the advice, but the reality for the social platforms is that this lack of tracking is a problem and it has to be a guiding reason for why Facebook has been so opaque on data. Its GDPR permissioning has led to an ICO investigation and contributed to widespread criticism from MPs that more needs to be done to regulate the internet.
This leaves Facebook navigating the tough line between finding out all it can about users across its platforms and avoiding further sanction. It has already been fined for breaking its word once, and the tide is most definitely turning against its privacy policies in the EU.
So the question is -- as consumers choose to go private -- does Facebook dare follow?