Design AtlasAn icon metaphor borrows the picture of an unrelated physical object and lets the role that object used to play stand in for a new function. The floppy disk on a save button is the textbook case — most users today have never touched a real one, and the "this shape = save" convention has stayed intact for over thirty years regardless.
Metaphors survive this long because an icon isn't really reproducing the object accurately — it's carrying the cultural meaning that object picked up over time. An envelope now means email more than it means an actual letter; a mechanical camera shutter shape means "open the phone's camera app." So the real test when picking a metaphor isn't whether the object is still in use — it's whether its silhouette is still a widely shared convention.
The trouble starts when a genuinely new concept needs a metaphor and there's no physical object to borrow — cloud sync, AI, anything abstract. There, an icon alone is often not enough to guess the meaning from, and pairing it with a short text label is the safer call.
When to use
Trust and reuse visual conventions that are already widely shared — a floppy disk for save, an envelope for mail. For abstract functions with no physical object to borrow from — cloud sync, AI — pair the icon with a text label instead of relying on it alone.