Can you assist with understanding why the unique visitors don't add up to the total but instances do?

I am using a date range of 6/14-6/29 (today).  They do line up if I use the 'instances' metric but I am, and want to be, using the 'unique visitors' metric.  Do you know why they do not add up with unique visitors?

My report has a total that is greater than the sum of the line items.  The reasons for this in the article you referenced are not applicable to my report.  It does not make sense to me why the total number of unique visitors would be greater since they should be falling into the bookmarked/typed cat...

My report has a total that is greater than the sum of the line items.  The reasons for this in the article you referenced are not applicable to my report.  It does not make sense to me why the total number of unique visitors would be greater since they should be falling into the bookmarked/typed cat...

Are you able to help me any further with this question?

What does this mean?