Duplicate content is an issue that commonly affects the rankings of websites in search engine results. Google puts negative weight on content that has been used on other websites or already written on your website. Duplicate content can be marked as SPAM by the search engines causing page ranking to drop or even cause the page to get blacklisted.

Website reputation is an important factor when it comes to search engine rankings. Having duplicate content can damage rankings if the content is found to be a copy of another page on the web.

Search engines use a syntactical comparison of content to check if the content has been directly copied and pasted from another online source. Even if other elements of search engine optimization are strong, duplicated content will not get a good ranking.

Slightly changing words and phrases trying to create unique content is not a smart move.  This process is known as content spinning and will hurt the quality rating of your web page. Many applications are used for content spinning or content rewriting, but using them can lead to lower rankings and possible blacklisting by Google.

Content optimization is the process of creating web content that is appealing to the search engines and the actual web users.  You cannot achieve content optimization through content replication. Understanding your target audience and developing quality content written for them is important to gain the best rankings on the search engines.

It is worth investing in a professional content writer for each page of your website to get the best visibility and drive more traffic to your website.

More Info on the negative effects of duplicate content.