When you purchase music, movies or books from Amazon or Apple’s iTunes store, you might be under the impression that that material is yours to enjoy forever; that’s how CDs and paper books work.

Anything digital is temporary, even if you clicked “purchase” rather than “rent.” One unfortunate side effect of that you won’t experience with a physical book or record: Your purchases may just disappear if licensing agreements change.

You also can’t sell or redistribute your ebooks, as you might with a physical copy. Apple’s fine print states that the licensor “reserves the right to change, suspend, remove, disable or impose access restrictions or limits on any External Services at any time without notice or liability to you.”