👉 Interests. Interests does not equal making a purchase. Algorithms still give first priority to shows to those who have already bought on Facebook!

👉 High CPM. On narrow audiences CPM is higher because the audience is smaller! And the higher it is, the more the algorithm reads the signal that the audience is not interested in the content. Display will be more expensive and somewhere at the bottom of the feed, as FB gives preference to campaigns that produce results. 

Accordingly, it remains to pour on the broad and trust in the holy algorithms. Age, gender and metolocation are all that's needed. 

🤨If your focus is on scaling and you give the algorithm more room, content can find and build its own audience more effectively than with narrow targeting.