#1 on Google's list of priorities is to provide the best user experience possible. Since Google's main function is to provide answers to people's search queries they do not want to serve the same answer or content over and over in the search results. Google strives to solve this problem by having its algorithm determine which content is the original and awarding it with a higher ranking than other "copy cat" sites.
How Unique Content Launched Us To Page 1
I encountered a duplicate content problem recently with a client who had difficulty ranking for some products. After using the following tools I found that nearly all of the content on the product pages came from the manufacturer descriptions that were copied and used across the web.
I found that bigger brands carrying the same product with the same description were trumping my client's site in rankings. Once I noticed this I had the content re-written on the page. Re-writing the content resulted in the page quickly moving from page 5 of Google to page 1 for several keywords we were targeting.
3 Tools to find duplicate content
1) Google Search - Quick Search Check
The fastest way to check and see if your content is original is to take a sentence of text and place it in Google Search.
Make sure to "put the content within quotation marks" to have Google look for that exact phrase.
2) Copyscape - For Stolen Content
Copyscape is a great tool that allows you to drop in a URL for free to find where else that content is found on the web. I especially like how Copyscape gives you a percentage of the page that is duplicated & actually highlights the duplicated content on the page. There is also a premium version that will monitor your content for you.
3) Screaming Frog - For On-Site Duplicate Content
A common problem that sites run into is having duplicate problems on their own site. Whether it be duplication of titles, meta descriptions, or even having URLs that need to combined (canonicalized).
I Found The Duplicate Content, Now What?
The kind of duplicate content that you find determines how you handle it.
Unique Content Problems- If the problem is because your content isn't unique, I recommend investing in creating quality unique content that Google and your users will find valuable.