The Search Engines are intent on eliminating duplicate content from their indexes. Why? Because finding multiple versions of the same thing, instead of unique content, gives users a bad search experience.
The Search Engines claim that they do not penalize websites that contain duplicate content. Instead, after deciding which page gets to stay in the index, they simply filter the offending pages out. However, I think anyone who has a website would consider it a penalty to have their pages removed from the results.
Duplicate content is eliminated from the index whenever it is detected, which may be during crawling, indexing or ranking. If you have duplicate content that has not yet been flagged, you’re playing the odds. Expect that sooner or later the Search Engines will find it and filter it out.
So, if you have pages on your site that are copies of other pages on your own site or other websites, you should take the time needed to make it unique. Otherwise, neither you nor anyone else may see it in the Search Engine Results Pages.