If you didn’t intentionally copy someone’s website, then it’s very unlikely for you to get a duplicate content penalty. If you have did copy large amounts of other people’s content, then you’re walking a fine line. This is what Google says about it: “Duplicate content on a site is not grounds for action on that site unless it appears that the intent of the duplicate content is to be deceptive and manipulate search engine results. If your site suffers from duplicate content issues, and you don’t follow the advice listed above, we do a good job of choosing a version of the content to show in our search results.”