When I worked as a news reporter, it used to make me testy as a wet cat when someone would regurgitate an idea I had retailed to him/her ... under the pretense that the idea or thinking was their own. By extension, it used to put a burr under my saddle to hear someone expatiating ideas they had clearly read in a book or heard on the evening news. There was never any attribution or nod to the source of the presentation ... and I thought it was galling and gutless ... and, of course, common.
Nowadays I think there's something to be said for recognizing:
1. All thinking is original thinking.
2. There is no such thing as an original thought.
3. And whatever thought there is, it most assuredly does not belong to me.