I asked this question here before, but I think I made it sound too complicated, so didn't get any answers. I could do with your opinion/advice, so here it is again:

I have included a direct quote from someone's paper in my thesis. A year or so later, I read a book chapter by someone else, and I found that article very useful so I cite this guy a lot in my thesis. But somewhere in his chapter he uses the exact quote from this first writer. I am so paranoid about plagiarism. I was so happy to discover that quote myself in the first place to be honest, but should I reference him instead just to be on the safe side?

Sorry if this sounds like a stupid question but I couldn't make a decision. :$

If it was me, I would quote the first author where you originally found the quote - because that is what happened. You found the quote by yourself before you read the second author.

I always primary reference - as if anyone will know! unless its an article that was printed 100 years ago or something and is out of print.

Could you add a little more to the quote to make it clear you got it from the primary source and haven't just copied from a secondary source? or add more to the context around it that ould only come from the primary one?

Otherwise stick to using the primary source, this is where you got it from, and unless someone is very familiar with the book chapter they wouldn't know the same quote was used.

Thank you for the replies. Good idea Catalinbond; I'll check if I can include more.