It's not just artists/creative types though, it can show up in anyone, whether they're a high performer or even those doing more menial jobs. I've seen it often in people around me.
This is an interesting excerpt
article about the impostor syndrome and high performers.
There's more in her book, but this sums it up.
On the other hand, when you look at someone else's work, you see a finished product, on its own terms. You know that there was work behind it, but that idea isn't internalized. You don't see how this or that idea comes from this or that source of inspiration, you dont see the mistakes and problems and struggles and failed ideas, you just play the game. It's like a magical, mysterious little thing that came out of nowhere.
I used to struggle with this a lot too, I think it's sort of connected to our innate tendency to jump to conclusions.