In 2014, a Senior Android engineer was tasked with building a new Android app in five months by mirroring an existing iOS app, only to discover the iOS app lacked user behavior tracking, leading to challenges in understanding user interactions and preferences. Without tracking data, the team inadvertently replicated iOS app mistakes and built features users didn't need, relying instead on web data that misrepresented mobile user behavior. The lack of tracking also resulted in the misprioritization of features based on incomplete feedback. Eventually, the team shifted focus to implementing comprehensive tracking, enabling them to better understand user behavior and prioritize features that mattered, resulting in higher app ratings and user engagement. The experience underscored the importance of incorporating user behavioral data from the start to make informed, user-centered development decisions.