The Keen2 wearable wants to train you to stop body-focused repetitive behaviors, but there’s little evidence to show that it works — Body-focused repetitive behaviors, or BFRBs, are common, but massively under-studied, disorders in which people repeatedly touch their bodies in ways that can inadvertently cause physical pain and harm. People with trichotillomania, which is perhaps the most well-known BFRB, pull out their hair (on their head, their eyebrows, or their eyelashes)…