The document on your desktop opens perfectly, so you put it on a USB drive for tomorrow. On another Mac, the file cannot be found. One possible explanation: you copied a Finder alias, while the document itself stayed behind.
An alias points to an original item. Opening it opens that original; making another alias does not create another independent document. This is useful for reaching a project quickly, but it changes what you need to check before a handover.
Find what the icon actually opens
Select the alias in Finder and press Command-R to reveal its original. Check the folder and drive you reach. If it is on an external disk, connect that disk first. A missing target is a reason to locate the source, not to assume the alias contains a recoverable copy.
For a concrete example, imagine a desktop alias named “Workshop notes” pointing into a folder on your external drive. To give someone the notes, copy the document from that original folder into a clearly named delivery folder. Keep the original while you check the result.
Check the delivered files
Inspect the delivery folder itself, then open the copied document there. For a handover to another person, ask them to open their received copy before treating the transfer as complete. A successful test on your own Mac can still depend on a target available only to you.
Use aliases for navigation. For a backup or handover, identify the actual files and verify the copies you intend to keep.