I'm sure I've said this before, but this idea has a pretty good repeatability disclaimer built into it..
The idea or meme is that any good idea that someone has is almost certainly also in someone else's head, and was probably even in someone's head who lived a long time ago and wrote a book about it. This can be discouraging. BUT, it shouldn't be if we think about ideas like children in an evolutionary sense. People are not discouraged about having kids simply because other people have also had kids. Someone's own kids are likely to be pretty darn similar to everyone else's kids (as humans, we are really good at noticing the subtle differences, but to an alien, I suspect humans would be really hard to tell apart), but we hope that our kids are a little bit different and a little bit better. So it is with ideas. Our ideas will inevitably be extremely similar to other people's ideas, but not completely the same -- there will be subtle nuanced differences in our own version of the idea -- and we hope that our ideas survive and reproduce.
It's good for people to have the same ideas as other people. This is the nature of the evolution of ideas. It shouldn't be discouraging. And we shouldn't discourage it by saying that people need to have "novel" ideas.