There are various reasons behind deletion of memory card files. One of the major reason is accidental deletion. While previewing some important files on the card you may hit the delete all button by mistake and thus in that way it is possible to
recover lost data or files from sd card for android or camera
Once you realize you've deleted a file, DON'T TOUCH ANY other file on that drive. That's because, when you delete a file, it's not really erased from the drive, instead, what the operating system does is to erase the "index" entry for that file (the location on the "drive map" where the actual file is located),