As far as here on the Hub Pages community, I had one issue with duplicate content when I first started.
I didn't know that all the articles written here on Hub Pages had to be original work. In other words, I tried to republish an article that I had already written for another platform and publish it as is.
I was given a prompt that said the article didn't meet the criteria for original work and any subsequent problems would bar me from the Hub Pages community.
Now, I understand that any previously written work has to be reworked and/or have a completely different angle.
As a writer, in general though, is it extremely difficult to come up fresh and new ideas all the time.