McElroy’s debut novel, “The Atmospherians,” told the clever but slightly insiderly and overfreighted tale of a wellness cult designed to cleanse men of their toxicity. “People Collide” is a more agile, universal book, with its title alluding to the randomness of human connection. It’s a variety of rom-com, really, that somewhat lost art. “Circumstances pinball people together,” the narrator declares. “This is called fate because chance is too scary a word.”