Sometimes a floppy disk (or other magnetic media like it) won’t read or write properly. Specifically, a format won’t work an gives various errors such as Unable to write track 0 or opening the disk in a hex-editor returns a read error.
I have always wondered if using a strong magnet (like that from the back of a car speaker) would be able to “re-initialize” the magnetic elements in the disk so that it can work again.
Googling it today only finds some discussion about disks that are corrupted by a magnet needing to be re-formatted, implying that a format can initialize such a disk. However I recall from the old days that floppies had tracks “printed” on them and a magnet could mess that up, preventing them from being used.