title_body: I can't find the mobi format ebooks I copied from my computer to my kindle via usb, what should I do?
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.