Here's how notifications work on the Apple Watch: When a new one comes in, the "taptic engine" — a linear actuator — literally taps you on the wrist to let you know about it. There's no loud buzzing to draw anyone else's attention, just a subtle but recognizable tap, designed for you and you alone. Meanwhile, the "short look" for the notification provides a minimum of information. Nothing that anyone could oversee — just the icon for the app and a brief bit of context as to who or why.
If you lower your wrist, it goes away. Keep your wrist raised or tap the notification, and it expands into a "long look" to give you more details. It's the kind of staging that respects that with greater intimacy comes greater responsibility. And I hope it's a sign of more features to come.