Presence is not the same as usefulness
Software often proves that it is working by showing more software. Another panel appears, another status animates, and another notification explains a thing the user already understands. The interface becomes a running commentary on itself.
In spatial computing this problem is physical. Every surface competes with a room, a person, or an object that already matters. A window can be perfectly rendered and still be in the wrong place. The cost of unnecessary interface is not only visual clutter; it is attention taken away from the world.
Disappearing requires confidence
An interface can become quiet only when the system has a reliable model of state. It needs to know what happened, whether the action can be reversed, and when the user actually needs help. Removing a confirmation without improving those foundations is not simplicity. It is missing feedback.
The best disappearing interactions preserve an escape hatch. They make the common path immediate and the uncommon path discoverable. Undo is often more humane than asking for permission at every step. Clear history is often more useful than a permanent status badge.
Design the return
If an interface disappears, its return matters just as much. The user should not have to remember a secret gesture or hunt through a menu to recover control. The system should reappear at the moment of uncertainty, in the place where the question occurred.
I like products that feel calm because they have done the hard work, not because they have hidden the machinery. The interface is still there. It simply knows when it is needed.