It's incredibly difficult to project breakouts before they happen. When I looked at fantasy football sleeper columns in 2015, I found that they were mostly useless. Even if a player plays well in a small sample or exhibits some level of performance that seems tantalizing, the short season and high attrition rate create obstacles in the way of some of the most sure-fire breakouts.
What's easier and more reliable, instead, is looking at last season's breakouts and figuring out which of those seasons are likely to recur the following year.