But once you know how to do it (it's swiping from right to left in a chat screen, by the way) it's a genius use of touch movement, right?

I'm torn about this - it's annoying that it's hard to discover, but I also hate when an app gets all up in my face about how to use its features - I usually open an app (especially a utility app like iMessage) with a specific intent and having the app interrupt that intent to tell me about itself is annoying.

I also have the perspective of being an engineer who builds interfaces. I think these are just hard problems and these kinds of pain points are inevitable as we continue exploring interfaces. I mean, the door is an interface that has been around since at least Egyptian times, and people still screw up affordance with it (how many times have you pulled a handle on a push door?)