Forrester Research conducts an annual consumer satisfaction survey called the Consumer Experience Index.  

In the survey, they ask customers to rate their experiences with various companies from 1 (very bad) to 7 (very good).

When collecting the data, they categorize the responses into three groups:

Group A (champions)—clients with a score of 7.
Group B (positives)—clients with scores 4 – 6.
Group C (negatives)—clients with scores 1 – 3.

When presented with this data, companies either attempt to eliminate the negatives (turn 1 – 3s into 4s or higher) or elevate the positives (turn 4 – 6s into 7s).

Which is a better strategy?

On almost every performance metric, spending time and effort on “elevating the positives” produces better results.

In fact, Forrester estimates that companies earn 9 times more revenue by “elevating the positives” than by attempting to “eliminate the negatives.”

Is it possible this consumer retention principle would also apply to agent retention?  

I don’t know of anyone who has specifically researched this topic, but I suspect it would.

Since you only have a limited amount of time to spend on retention, dedicate it on trying to convert your positives into champions.

It will produce a better return than trying to save your negatives.