Does this ever happen to you?
You have a thought, you say this thought aloud. It sounds nice. You say it to other people. They are amazed at your brilliance. And then you realize someone said it already and you just happen to have picked it up and thought it was you who came up with it?
I just had a thought. "Literature is my sandbox." I thought, "Wow, this sounds great. I'll share it." I shared it and picked up my book to read (An Unnecessary Woman by Rabih Alameddine) and BAM!!! I realized it's the character in the book who said it. So I quicky deleted the post.
And here I thought I was so smart...