[OkayPhysicist]

IMO, the overlooked big innovation of Snap, and the thing that got them their initial popularity, was their absolutely arcane interface. They've done a lot over the years to make the app easier to use, but in its early days, there was an almost toy-like quality to trying to figure out the various features and functionality. That acted as a selling point to the teenage demographic: not only did friends showing each other how to access some practically secret part of the app act as viral advertising, it also kept your parents off the app.

It also acted as an overt anti-Facebook, in an era where that was a growing trend: No, and then limited, broadcast communication versus FB's "tell everyone everything" defaults, ephemeral messages in stark contrast to FB's "hey, remember this inane thing you said 3 years ago", and a culture of communicating asynchronously with a face attached.

This (perceived) lack of a panopticon made Snapchat a much more appealing form of social media. IMO, it's still one of the better ones.