Retention is the most important metric for a new feature or a new app. Focusing on acquisition or monetisation can seem like a more exciting problems to solve but solving for retention is most critical.

Read this thread and you will be convinced at the end of it. 1. Retention can in fact drive acquisition
For many products, retention has a double effect. More users you retain, more key actions are performed like sharing, inviting, word-of-mouth, or creating content and it sets off a self-reinforcing cycle that drives acquisition.