Fitness is fantastic but there's one thing Apple Watch does that really feels like magic.

"How do you want to pay for that?" "VISA." Tap. Beep. "Wow, that's amazing. Is that your watch?" Smile. "Boarding pass?" "On my watch!" Scan. "Wow, that's incredible! Apple Watch?" Nod. "Here's your coffee!" Scan.""Wow! I've gotta get one of those!. "Want me to pay for gas?" "Nah, I got it." Tap. "What is that, magic?"

Long before Watch was even announced, I began to wonder about what I'd want from Apple on my wrist. Convenience was my killer feature. If Watch could save me from having to reach for my phone in order to do a few important, frequent, yet simple things, it'd be the equivalent of my phone letting me leave the house without my computer.

But convenience is a hard feature to demo in the wild.

When iPhone first came out, it was cool but it wasn't some abstract coolness that made people's eyes light up. It was the specific coolness of pinch-to-zoom in Photos or Maps, or Cover Flow in iPod. Those were immediately, undeniably cool.

When Apple Watch first came out, I had trouble finding a similar demo. It didn't help that Watch wasn't a minimally delightful product in the same way as iPhone. Apple introduced it with a bevy of features which made isolating one as the go-to demo harder: Mickey may have made people smile but it didn't make them want to immediately rush out and buy.

With Watch Series 2 and watchOS 3, Apple found their focus in fitness. The product still does a lot more, of course, but the messaging and advertising has been all about those rings and workouts.

For all the greater clarity and coherence, though, the Activity Rings and Workouts still don't make a great demo. Don't get me wrong — I love closing all my Activity Rings every day and the motivation that the new sharing features provide, but if you just show those rings to people they don't get it at a glance, not like they did with pinch-to-zoom.

Then, over the last few weeks, something started happening. I went to to Apple Pay for lunch at a local restaurant and instead of the man saying "Wow!", the man behind the counter held up his own Apple Watch. Instead of the woman at Air Canada gate being shocked when I scanned my boarding pass, she held up her Watch to show me she'd just gotten one too. Instead of the guy at the Starbucks drive through thinking my Apple Watch was cool, as he reached out to scan my digital card, I saw he was wearing one of his own.

A photo posted by Rene Ritchie (@reneritchie) on

By some estimates, Apple sold 5.6 million Watches over the holidays — a quarter where Watch was and remains bafflingly constrained. That could bring the total number of Watches sold so far to a 25 million. I'm sure the new fitness focus and campaigns had something to do with that and I'm sure when people use those feature they love them.

But Apple Pay and Wallet? That's the "Wow!" moment. That's the demo I'd been looking for and the one that's been right in front of me this whole time. It's what my friends, who recently go Apple Watch, are messaging me all excited about. It's what the guy at the coffee shop counter loved when I stepped up, tapped, paid, and was on my way while the person beside me was still counting out cash. It's the magic.

Fitness is cool. Fitness is fantastic. Fitness absolutely makes our lives better. I love the first and latest ads Apple's done for Watch around fitness. But I can't help but wish for a really great Apple Watch ad centered around Apple Pay and Wallet next.

Paying at retail or at a drive-through or while jogging past a corner store. Getting your movie tickets, boarding your plane, or picking up your loyalty points. I'd even fold in opening the door to your hotel room and unlocking your Mac. An ad like that, done with the usual Apple panache, would make the convenience of Watch manifest.

Apple has succeeded in making paying for things not just cool but fun as well. Paying for things. Fun. That's something to show off.

My guess is we haven't seen a lot of this yet because the U.S. has only just begun to adopt tap-to-pay technology. That'll change, though. And as it does, I think we'll see a lot more of those "wow" moments, and Apple will sell a lot more Watches.