title_body: I can't find the mobi format ebooks I copied from my computer to my kindle via usb, what should I do? Transferring ebooks in mobi file to my kindle used to be hassle free. I just drag it to the "documents" folder and voilà! They're there. 
  
  What happened yesterday was different. I tried to move mobi ebooks to my kindle. The books were  transferred fine, I can see them on my kindle drive on the computer. The problem was when I opened my Kindle to arrange the books I transferred, they weren't there. I tried reconnecting my kindle to the computer and the books are still there. I don't know what's wrong.
upvoted_answer: File size can be an issue. I've found that if the book's file size is greater than 50MB, the file will transfer to the documents folder on disk, but not appear on the kindle. In my case, I used Calibre to convert mobi to azw3, which reduced the file size, and the book then appeared on my kindle.