Teenagers often do terrible things, to themselves and to others; the road to becoming honorable adults is sometimes paved with a few stones of cruelty. In the sweet, smart Netflix-produced romantic comedy Sierra Burgess Is a Loser, Shannon Purser (who played cult favorite Barb in Stranger Things) stars as high school senior Sierra, a bright, reasonably confident young woman who knows she falls short of the beauty standards that teenagers set up for themselves: she’s curvy and a little socially awkward, but mostly she’s getting by just fine.