Set in the late 1970s, Maya Forbes’ new movie stars Mark Ruffalo as a bipolar Boston dad who takes dubious custody of his two young daughters while their mom, played by Zoe Saldana, gets her MBA in New York. This heartfelt, openly autobiographical, faultlessly cast work is Forbes’ debut as a writer-director. So why does it seem so bogus? Could she be too close to it? Surely it is not on purpose that Infinitely Polar Bear seems to have paid more attention to recognizable period art direction than to recognizable humanity. Of course Ruffalo as a lovable mess is a proven movie commodity, but here his usual rumpled charm becomes brittle and unnatural, cheapened by distracting cigarette shtick. We see less of the depression than the mania, and both are played for broad, nonthreatening laughs. That’s a disservice. Overstuffed with scene-transition music cues, the movie plays out as a clump of episodes in search of dramatic shape. Its organizing principle seems to be a fear of lapsing into anything other than just a feel-good movie. More directly addressed, that fear might be good material in and of itself. Meanwhile, on-the-nose acknowledgments of race and class and gender constraints seem merely like festival-acceptance touchstones, and Infinitely Polar Bear just rolls along, leaking all reserves of authenticity. You could argue that feeling aimless and oddly hollow actually is the right way for a film to reflect the close observer’s experience of mental illness. But that demands more awareness and finesse than Forbes has mustered here. This movie must have meant a lot to her, but her defensive stance keeps it from meaning enough to the rest of us.