See my comment here [0] with its genuine, but as yet unanswered question:

  If you hit space, how do you know
      you end up seeing every slide?

Every seems to be chipping in with these navigation hints, and that's great, but no one seems to answer my question. The site seems to be a triumph of presentation over usability, and I'd really like an insight into the minds of those people who think it's all obvious and usable.

For example, someone else said[1] that if you hit ESC you get an overview. How do you find that? What if you don't have an escape key, such as on my tablet?

I'm not trying to be grumpy or anti-anything, I'm trying to gain an insight into how people think this is a good thing, and to provide, in return, an insight into why I think it's unusable.

[0] https://news.ycombinator.com/item?id=11653447

[1] https://news.ycombinator.com/item?id=11653323