The problems faced by gesture developers remind me of similar issues that arose during the early days of development of the GUI. Thus, in the development of the early Xerox PARC systems, when one moved the icon of a file across the screen to a file folder, it was natural that the icon would disappear into the folder. Similarly, when a file was moved to the trash, it was natural that the icon — and the file — disappeared from sight. But this movement principle got into trouble with the printer: Moving the file to the image of the printer caused the item to be printed, but it also caused it to disappear from the screen. Much rethinking took place then. Much rethinking is required now.

What gesture signifies copy rather than move? | donald a. norman, natural user interfaces are not natural