Depends. They certainly lose a potential sale from some people, but many people who pirate books never would have read it if they needed to pay for it. Be that because of a lack of money or a lack of interest. Same with games and shows. So no lost sales there.

You could even argue that pirating helps with sales by causing people who never would have read the book otherwise to discuss it with friends or strangers online. I personally think that argument is a big stretch, but it's not entirely wrong.

But yeah, more pirates should be willing to support authors of books they like. If you think they deserve it, buy the ebook even if you've already read the whole thing.