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Margot is shy and quiet, until you get her talking. If you’re a good-looking young man who flirts with her, she’ll flirt right back, and she doesn’t mind if the flirtatious talk begins to edge into naughtier territory. She’ll blush, but she won’t back down. She likes the sexual innuendos and the “innocent” touches; skin on skin feels so right.

Margot is married. She loves her husband. She loves when he talks to her, and does things for her. She loves to touch him, and, especially, she loves to be touched.

Margot is unhappy. She doesn’t know why.

The swirl of emotions captured by actress turned writer/director Sarah Polley in Take This Waltz is, by turns, seductive and frustrating and puzzling. Polley spells out 95% of the movie in slow, methodical order: Margot (Michelle Williams) is a travel writer. She is attracted to Daniel (Luke Kirby) while on a trip. They return home. Daniel has moved in across the street from Margot. Margot is married to Lou (Seth Rogen). Lou is a cookbook writer. Lou cooks chicken. Daniel is an artist. Daniel owns a pedi-cab. Lou’s sister Geraldine (Sarah Silverman) is an alcoholic. Daniel is attracted to Margot. Daniel pursues Margot. Margot likes being pursued. Margot resists being pursued.

The push/pull between Margot and Daniel is defined by their secret meetings and flirtatious talk, which becomes more overtly sexual over time. Lou is oblivious.

In one of the more obvious examples of Polley’s inclination to tell and show — to really drive her points home — Margot openly wonders about the advisability of pursuing an exciting affair vs. the dependability of a less-than-thrilling long-term relationship. She discusses this with Geraldine and another friend while they are sharing a group shower after a swim class.

Polley forthrightly shoots the scene as the young naked women soap up and rinse off, and then soap up and rinse off again, and then shows them exchanging glances with another group of friendly women in the other part of the open shower, a group of older, heavier women, wrinkled and shriveled in the way that is destined for all flesh. And then one of the older women says, in effect, ‘This is what happens to you when you age. Things change. Better get used to it.’ And Margot wonders what she should do.

Margot, embodied by Michelle Williams with incredible nuance and tenderness and confusion, is not happy, but she doesn’t know why. She’s been married to Luke, a kind and loving man, for years, but prefers joking and flirting to any sort of true communication with her husband. In her conversational exchanges with the soulful-looking Other Man, Daniel, we never hear her reveal anything about her inner life, or her past, or even much about her present unhappiness with Luke.

All of which makes the movie feel irritating and petulant for much of its running time, because Margot is acting in such a selfish manner. It’s as though Polley is justifying adultery, which, personally, caused me to reject it on a knee-jerk level. Frankly, characters who refuse to accept responsibility for their own actions are a huge stumbling block for me, especially when they are presented as some kind of suffering heroine or tragic hero.

The movie takes a turn at a certain point, however, banking steeply upward toward a more poetic, less prosaic view of Margot and her attempts to wrestle with her own emotions. And though my initial conclusion was more negative, I’ve wrestled with my own feelings in the days since I saw the movie.

And I’ve come around to this notion: Yes, Margot fails to impress me as any kind of praiseworthy character (though Daniel is a nastier sort, in my book). But Take This Waltz is not necessarily holding her up as someone to be praised. I think Sarah Polley is suggesting that it’s really, really hard to see ourselves as others do, and even more challenging to look into our own souls and see what sort of person we are.

To my complete surprise, that makes Take This Waltz one of the more troubling movies of the year.

Take This Waltz opens today exclusively at the Landmark Magnolia.