If I observed a 10% decline in DAU while serving as the Product Manager for Coinbase, my initial step would be to thoroughly examine our analytics tools to determine whether the drop affects all user segments, regions, and product lines, or if it is limited to a specific group. This comprehensive analysis would provide insights into the severity of the problem. Should the decline be apparent across all user segments and product lines, I would look into whether there are broader market trends contributing to this situation or if recent updates to our app have led to user dissatisfaction. Additionally, I would review app crash reports and customer service inquiries for further insights. If, on the other hand, the decline was confined to a particular cohort, I would dedicate more time to understanding the needs and behaviors of that specific group to identify the issues. Gathering customer feedback, reviews, and conducting user interviews, if needed, would also be beneficial in uncovering the root cause. Once the potential issue is identified, I would collaborate with my team to develop an effective strategy to address it. This could include A/B testing modifications, implementing updates, or launching marketing campaigns to restore user engagement.