Why the recovered files cannot be opened?

A file is saved as 2 parts on the storage device: directory info (which is comprised of the file name, timestamp and size info, etc.) and data content. If the files with original file names and folder structures cannot be opened, one possible reason is the corrupted directory info. There is still a chance to open it again after repairing it with some tools. But if the data content is damaged, there is no way to open it again.