Most often, duplicates are just multiple entries for the same name.

For example, you may have one entry like this:

Amy Lee
amy@lee.com

And one like this:

Amy Lee
amylee@yahoo.com

Our software makes the educated guess that these two email addresses belong to the same person and proposes to combine them into a single entry:

Amy Lee
amy@lee.com
amylee@yahoo.com

But of course, sometimes you DO know two people with the same name. (Hello Serge Grzbjreneski—right??) And sometimes you may have a good reason to separate entries that seem like duplicates. This is why your potential duplicate entries appear one by one for you to review.