Increasingly, people are amassing long term physical activity data which could play an important role for reflection. However, it is not clear if and how existing trackers use their long term data and incomplete data is a potential challenge. We introduced the notion of adherence to design iStuckWithIt, a custom calendar display that integrates and embeds daily adherence (days with data and days without), hourly adherence (hours of wear each day) and goal adherence (days people achieved their activity goals). Our study of 21 long term FitBit users (average: 23 months, 17 over 1 year) began with an interview about their use and knowledge of long term physical activity data followed by a think-aloud use of iStuckWithIt and a post-interview. Our participants gained new insights about their wearing patterns and they could then use this to overcome problems of missing data, to gain insights about their physical activity and goal achievement. This work makes two main contributions: new understanding of the ways that long term trackers have used and understand their data; the design and evaluation of iStuckWithIt demonstrating that people can gain new insights through designs that embed daily, hourly adherence data with goal adherence.