I loved this usability lesson from Michael McWatters. It showed me two things. First, even the most talented designers in the world sometimes develop software with UX issues. Second, it made me look at how you discover a design problem and tackle the issue with a simple fix. I didn't know what a norman door was either. Good lessons here.
iOS 10 Control Center has a Norman Door by Michael McWatters
Maybe I'm showing my age a bit, but I'll admit that I didn't really "get" Snapchats design at first. In fact, I don't think I fully understood it until I read this article. It's a good history lesson on intuitive design and why shareable design, like Snapchat, is hot right now.
Snapchat does this brilliantly, because each of those seemingly obscure features is an opportunity for its users to show their friends how to do something cool. Showing your friends something cool can increase your social standing, or maybe it just gives you a good feeling.
Intuitive Design vs. Shareable Design by Josh Elman