A Share Is the Only Engagement That Leaves the App
Open the share sheet on any TikTok and look at what is actually on it: direct message, WhatsApp, Instagram Stories, copy link, and a dozen other destinations. Most of those take the video somewhere TikTok has no visibility into.
This matters for two reasons. The first is reach of a kind no other signal produces — a video sent into a twelve-person group chat has just been put in front of twelve people who were not going to be served it by any recommendation system. Some of them will open it in the app, and that traffic arrives already primed, because a person they trust sent it.
The second is what the act tells TikTok. Sharing is the most effortful common interaction on the platform. It requires deciding the video is good enough to attach your name to and interrupt someone else's day with. Videos that accumulate shares tend to be the ones that break out of their initial audience cluster, because sharing is the behaviour that most reliably predicts a video being worth showing to strangers.