When I first heard rumors of Apple Watch, I thought convenience would be its killer feature. Personal computers couldn't do everything mainframe computers could, but they saved you a trip to the offie. Phones couldn't do everything PCs could do on the desk, but they saved you having to go back to your desk or laptop. And watches, certainly, couldn't do everything phones could, but they could do brief, frequent, important tasks well enough that they'd save you having to reach for your phone.

In some ways that's panned out. Notifications on Apple Watch are easily glanceable, unlocking your Mac or Home is near effortless, and Apple Pay on Apple Watch — in areas blanketed with tap-to-pay, like where I live — means carrying cash or cards is almost a thing of the past.

But notifications weren't and aren't granular or prioritized enough, Apple's identity system isn't complete enough, and mobile payments aren't ubiquitous enough. And it's still a watch that, absent you turning your wrist or tapping the screen, can't even constantly show you the time like a watch. Convenience, alone, wasn't enough.

Neither was fashion. A clever band and even link swapping system that over a hundred years of traditional watchmaking couldn't come up with, designs from Jony Ive and Marc Newson, materials from gold to ceramic, and partnerships with Hermes missed the mainstream.

Fitness, though… that became key to Apple Watch's success. Bodies are fed as much by motion as they are by food, and filling your rings is a great motivator to keep on moving. Likewise, minds digest through stillness, and the breathing app helps make sure you always take the time to save your cache to disk.

It's the ability to track indoor and outdoor workouts, though, from walks to runs, swimming to skiing to rolling, with data on time and pace and, critically, heart rate that make Apple Watch compelling. Add partnerships with Nike and integration with exercise machines through GymKit, and it starts to go beyond fitness fad and becomes infrastructure.

And that's especially true as its gone from water resistant to swim proof, from being tethered to an iPhone to being LTE-capable-ish all its own, and from being Apple's only wearable to pairing with AirPods to give us a glimpse of a truly wireless future.

But, through it all, something else was happening…

Apple Watch saves lives.

Of course, computers save lives and phones absolutely save lives. They do it every day. But because Apple Watch is attached to you, it's more likely to always be with you, even when your phone is thrown out of reach. And because it's now swim-proof and LTE-enabled, you can use it not only when you don't want to reach for your phone… but when you can't. When you're in an accident or when you're in the water. And whether it's through the newer 911 emergency feature, or more traditional messages or calling.

And because it has features like the heart-rate monitor, it doesn't have to wait until an emergency to help you — it can let you know when there's about to be an emergency. And I think it's just the beginning.

Jeff Williams, Apple's Chief Operating Officer, runs Apple Watch at Apple. But what he really runs is Health. So when you look at what Apple's doing, including recent features like connecting health records, and when you look at rumors, like blood sugar monitoring, it's not hard to imagine that, as good as Apple Watch is for fitness today, in the future that'll just be one small part of how great it is for health. As good as it is with AirPods for Apple Music as a service now, it could be even more critical with a range of wearables for Apple Medical next.

Tap to pay is the best transactional experience out there, and Apple Watch helps ensure it's private and secure. Tap to check into a clinic or doctor's appointment or hospital, connecting all your medical care and insurance, and all your medical history, medication, and allergies, would be world-changing.

And, while phones are currently the most important devices we own, it's why I think Apple Watch could ultimately be even more important.