Back in the height of growth hacking, everyone wanted to emulate Facebook and its 7 friends in 10 days metric. Facebook noticed that there was a strong correlation between a user achieving 7 friends in 10 days and retaining long term. Then, they built their entire onboarding around this metric: every new user was pushed to achieve 7 friends on the platform in their first 10 days. Many ascribe Facebook’s insane growth to this strategy.

This metric encourages the company to build experiences that increase engagement for new users, and also encourages the building of experiences that push new users to invite other people to the platform. This is striking, and positions Facebook to become a highly retentive and viral product.

Now, a lot of people attribute the success of this metric to the vitality of the Facebook Feed. If a user has at least 7 friends on the platform, their Feed will be fully populated and a lot more interesting. Thus, the user will unlock the core benefit of Facebook: keeping up with their social network.

In the time since, Facebook has come up with a number of clever hacks to keep the Feed entertaining: extra news stories, a friend of a friend’s post, a trending post are all inserted now. But it was TikTok that came up with an unprecedented change to a feed algorithm: show a new user posts from people they do not follow. Create an addicting feed instantly, without nudging the user to follow others first.

Instagram (to my personal annoyance) has recently tried to follow suit:

Instagram has started inserting suggested content into my feed, and that I took steps to remove suggestions from my feed (for only 30 days though, sigh). Whatever my personal complaints are, this is a great way to engage new users, and an innovation in onboarding for social networking.

However, with pre-populating feeds, companies are missing out on the opportunity to encourage users to invite other users onto the platform. Why bother inviting people to or following people on TikTok if TikTok knows what you like anyway? Is there really a benefit for following your entire high school class on TikTok, besides driving up your follower numbers? When I was in high school, I needed to friend all my classmates on Facebook in order to stay in the know. With TikTok, there is no reason to follow my friends: there are already people similar enough that are doing plenty of entertaining things on TikTok.

Without encouraging users to invite new people onto the platform, TikTok misses out on a whole avenue for virality. I suspect this is why TikTok ads seem so ubiquitous to me; they can’t rely on a friend of mine to bring me onto the platform, and instead they must use more traditional marketing methods.

Interestingly enough, I suspect Pinterest suffers from low virality as well as their ads seem to compete with TikTok’s ads. Pinterest also pioneered a way to populate their feed without much user input, but still gives users a questionnaire of what they would like to see when they join the product. Pinterest is not based around existing social networks but instead interests, and thus doesn’t give users a reason to invite their friends onto the app.

It isn’t a dire signal, however, when social media apps spend a lot of money on ad campaigns. TikTok clearly has a high user retention that bankrolls their user acquisition. We can assume that if TikTok is willing to pay a lot of money to acquire a user, that user is worth even more money to TikTok over the user’s theoretical lifetime.

That being said, it is always cheapest for platforms to have existing users bring new users onto the platform.