The following quotes from from Daring Fireball. Emphasis is mine.
It’s best to think of Apple Watch as having two modes: watch mode, and app mode.
You do not need to understand this to use the watch. Most Apple Watch owners will never really think about this. But this idea of two modes is central to understanding the design of the overall interaction model.
Then, further on in the piece:
Watch mode is where you take quick glances at information and notifications; app mode is where you go to “do something”.
Watch mode is where most people will spend the majority — perhaps the overwhelming majority — of their time using Apple Watch. App mode is a simple one-level hierarchy for “everything else”.
It’s so simple, he needs to dedicated a 1,500 word post to explaining how simple it is, and (apparently, possibly) more than 12 hours of cumulative podcast:
@parisba It’s quite incredible. I think he is approaching 12 hours of dedicated podcast to it
— El Coõko Ninõ (@dobes) May 22, 2015