It turns out that it all goes back to the playground. What did our moms tell us when boys teased us and knocked us down? “He only does it because he likes you!” This leads to two consequences. First, women lose the ability to apply common sense in interpreting the signals about level of interest sent by men. Second, men get positive reinforcement for sending those mixed signals. Add in a couple of doses of fear of getting hurt and fear of being alone, and a just a dash of fear of missing out on The One and you have “He’s Just Not That Into You,” a movie inspired by a non-fiction book inspired by one line on the television series “Sex and the City.”

On that episode, a man named Berger (Ron Livingston) took pity on a character who was coming up with increasingly far-fetched excuses for a man’s turning down her invitation to come up to her apartment after a date. “He’s just not that into you,” said Berger. This was a revelation. The episode attracted so much attention it led to a non-fiction book (written by a male-female team), and that led to this daisy-chain of stories about love old and new, sweet and sad, funny and wise.

At the heart of the story is Gigi (“Big Love’s” Ginnifer Goodwin), an ever-hopeful sort who is always willing to see the glass as half full even if there is nothing in it at all. He hasn’t called? He’s busy at work or he had a sudden business trip. Or maybe he forgot her number. She is helped in this romantic delusion by her friends, who try to cheer her up by persuading her that men behave like this all the time when they are interested and they always have these hopeful little urban legends about someone’s second cousin’s college roommate who thought that a guy wasn’t calling but then they got married and lived happily ever after.

It takes a cynical bar manager named Alex (Justin Long) to give Gigi the movie title advice, and that leads to some more bracing honestly. It all boils down to this: the only signal that matters is the choices people actually make. If he wants to talk to you, he will call. If he wants to see you, he will make it unequivocally clear. Same for women, by the way.

Meanwhile, a young married couple (Jennifer Connelly and Bradley Cooper) is dealing with stress on two levels, external and internal. Their new home is being completely gutted and renovated. And he is feeling attracted to a vixenish young singer (Scarlett Johansson) and to the possibilities of a life without constraints and promises. An ad saleswoman for a gay men’s newspaper (co-producer Drew Barrymore) says that modern technology has just created more ways to keep from talking to each other — email, texting, voicemail, and myspace. She gets a lot of support and some good advice from her sympathetic co-workers. And another couple (Jennifer Aniston and Ben Affleck) gets along just fine on every issue except for one — she wants to get married and he does not.

You will get a sense for which side this film takes in the gender wars when you look at the cast — the big names and familiar faces are mostly on the female side. But the performers are all attractive and capable and director Ken Kwapis (“Sisterhood of the Traveling Pants”) knows how to keep several stories going at once. He manages his talented cast well and he skillfully handles the material so that it stays comic without losing sympathy for the characters. The film balances humor with some sharply observed moments and painfully familiar conversations that are sure to provoke some lively debates on the way home from the theater.