It’s widely known that Google isn’t a fan of duplicate content. If someone posts an article and a few months later it’s copied by 10 other sites, Google will try and find the most credible source and only display that one in the search results. The most credible source is usually the oldest one since they’re likely to be the creator of the content. The other 10 sites would only show up on the supplemental results which means they’ll rarely get any traffic.
So how can you avoid having your content being labeled as duplicate content? You shouldn’t copy an entire article from beginning to end. You can and are encouraged cite someone else’s content, but add enough text so that the post itself has enough unique content.