Plagiarism...

The plagiarism article was a good refresher on how to avoid making this big mistake in my writing. What I am curious about is: When does someone else's opinion become your own? I mean, most of my opinions on things come from hearing a whole slew of people's opinions and ultimately adopting one that I believe in. This article says plagiarism can be using someone else's opinion as your own. What if I come across someone's work who has the exact same opinion as me. So if they had it first, do I have to cite it? I don't know if I'm making sense here, it just seems like there could be some argument about this.

I promise not to plagiarize. I promise to cite direct quotations, and to paraphrase information in my own words and organization, and cite the source. And if I come across any quarrels about if what I'm writing is plagiarism or not, I will ask about it instead of taking the chance.