3D Touch is hard to discover. Simple as that. It’s been three years since Apple debuted pressure-sensitive screens and I still have conversations with my family about how to access what should be simple features … features that just so happen to be gated behind a firm press gesture.
Apple’s usage of 3D Touch throughout the system is inconsistent. that they artificially wall off features with 3D Touch gestures, when they aren’t needed at all. In Control Centre, you should be able to long-press on the platters to open them up. There’s no reason for this action to rely on pressure. Another case of this kind of misappropriation is the ‘Clear All Notifications’ button in Notification Centre. A long-press could serve the same job, and it doesn’t. That’s weird.
In the Mail app example, peek and pop previews do necessitate a sensitivity to pressure. You apply less pressure to display the preview, and press harder to commit the navigation. You couldn’t do this with a simple long press. The question is then is it a problem that many users won’t ever think to do this. I’d say it’s not, Peek and Pop is merely a shortcut and not essential. The primary action, viewing the email, is always available with a simple tap. A shortcut behaviour does not warrant a permanent visual indicator. The email summary cells can be swiped left or right too, but we don’t reach to put an arrow glyph on either side of the screen to hint at all possible actions. It’s just there if you need it.
A third class of problem is cases where the same on-screen elements respond to pressure and long-press interactions. I’ve observed that human dexterity is not as good as you’d think a modern species would be, and it’s hard for people to apply the correct amount of force. As such, elements supporting both long-press and pressure-based behaviours are frustrating to use. The gestures clash way too often in practice; users accidentally press in on the screen and cancel their long-press, for example. On the iPhone, the obvious example of this is the app icons. You can long-press to make the icons jiggle and enable icon re-arrangement, or force-press and show quick actions.
Ideally, these situations should be avoided altogether. Fortunately, it doesn’t happen too often in iOS. For the Home Screen editing, I think Apple should provide an escape hatch to smooth out 3D Touch misfires; with quick actions visible, some sort of button in the corner of the screen to jump into jiggle mode.
All this to say there are better ways to make 3D Touch more approachable than to put little decorations on every UI element that responds to pressure. Remove the places where 3D Touch is an unnecessary gimmick, and refine the interactions where it is actually useful. Find ways to bring important features that are currently ‘hidden’ behind 3D Touch actions into the main interface on screen — rather than add repetitive, redundant, visual affordances that most users would be blind to anyway.