Marco Arment on the Apple Watch's built-in Activity app:
The more I use it, the more I appreciate that the Apple Watch’s activity-tracking features are impeccably designed for effectiveness and encouragement.
There are other activity trackers, but a watch face is a perfect place for one: it has physical access to relevant biometrics and motion, it’s typically worn every day, and it’s checked regularly throughout the day so your progress toward goals is easily visible — satisfying if met, and encouraging if not (and you know before it’s too late). I don’t even want to spend much time awake without wearing the Watch because I want my activity to be counted.
I doubt Marco's story is unique, and that's a testament to the effectiveness of Apple's Activity app. The circle metaphor Apple has opted gives you great satisfaction when you fill up those rings and the regular achievements that can be unlocked gamify the experience, providing extra encouragement.
The next part of Marco's post is more profound. It's something I hadn't thought of, but I couldn't agree more:
The benefits of this at scale could be huge: consider the net improvement of millions of Apple Watch owners making small improvements to their health.
The Watch is Tim Cook’s product. And in the perfect Tim Cook way — subtle, understated, but incredibly powerful — he’s improving the world.