Retention compounds. A 10% improvement in retention often outperforms a 50% improvement in acquisition because retained users contribute repeatedly and refer.
If you retain 40% of users after month 1, you need to acquire constantly to grow. If you retain 70%, growth compounds.
Cohort retention: what % of users who signed up in month X are active in month X+1, X+3, X+6?
Get retention above benchmark for your category. Then scale acquisition.