The Drag and Drop Confusion
In macOS, dragging a file from one location to another using your mouse or trackpad usually results in a simple move operation. However, the operating system attempts to be “smart” based on the destination. If you drag a file from your internal hard drive onto an external USB drive, macOS automatically assumes you want to copy the file. Even more confusingly, if you hold down the Option and Command keys simultaneously while dragging, or if you drag an application out of the Applications folder onto your Desktop, macOS will automatically create an “Alias” (a shortcut) rather than actually moving the file. This can lead to massive frustration when you think you have moved a large video file to an archive folder, but you have actually just created a tiny shortcut pointing back to the original.
Enforcing a Strict Move Operation
To stop macOS from making assumptions and automatically creating aliases or copies when you drag and drop, you must use a specific modifier key to explicitly force a standard “Move” operation.
Whenever you click and drag a file or folder in the Finder, pay close attention to the small icon that appears next to your cursor. If you see a green circle with a plus sign (+), macOS is going to copy the file. If you see a small curved arrow, it is going to create an alias. To override this predictive behaviour and force the file to simply move from the source to the destination, press and hold the Command (⌘) key immediately after you start dragging, and keep it held down until you release the mouse button. The cursor icon will strip away any plus signs or arrows, guaranteeing that the original file is physically relocated to the new folder without leaving any confusing aliases or duplicate copies behind.