Developed by way of the Sundance Writers’ Lab, writer-director Sara Colangelo’s debut feature elaborates on her 2010 short of the same name, and it’s not like Colangelo really needed four years and some palpably interventionist institutional permission just to repeat herself. But the full-length version of Little Accidents is its own story, about how the aftershocks of a fatal coal mine accident radiate along small-town socioeconomic fault lines, and it allows for a great breakout performance by newcomer Boyd Holbrook as the disaster’s only survivor, feeling pressure from his union to testify against a coal company executive (Josh Lucas). The supporting cast includes Elizabeth Banks, Chloe Sevigny, and Jacob Lofland, all respectable, but it’s Holbrook, precise and inviting, who most holds our attention. Actors do good work for Colangelo, who has a gift for small, tenderly expressed moments of human connection, and for knowing how important they are to the Sundance school of social anthropology. Her voice carries even amid the din of contrived class conflict with stakes raised to melodramatic levels, then underplayed as a kind of poker-faced compensation. If this story seems inorganic, or in any case less authentic than its well-observed atmosphere, at least the storyteller has seen and seized an opportunity. Here’s hoping she’ll have more.