New research suggests tracking healthy behaviour might make you more likely to indulge elsewhere. I like the basic promise of a Fitbit. That was my first fitness wearable more than a decade ago. But any similar wearable, for that matter. So, you walk more, sleep better. Pay more attention to what your body is doing. And improve stuff by measuring it. Right? That logic is intuitive enough that self-tracking got built into watches, phones, rings and fitness apps everywhere. But a new study...