I think "plagiarism" means a steal work or steal though.It is not make by your-self.You copy it came form other people.And It is not unfair for owner .they very difficult for get it.But you steal its easily .
For instance,In class you are steal ed examination or test paper by your friend.It's easily for thief because they don't invest for everything but they receive point.But you is difficult for it.you get lose time for read a book.It's Unfair for owner