Wearable devices, from smartwatches to fitness trackers, have become ubiquitous, continuously capturing a rich stream of data about our lives. They record our heart rate, count our steps, track our fitness and sleep, and much more. This deluge of information holds immense potential for personalized health and wellness. However, while we can easily see what our body is doing (e.g., a heart rate of 150 bpm), the crucial context of why (say, "a brisk uphill run" vs. "a stressful public speaking eve...