All of the characters are very odd people - Spoilers
Karen - She looks up the guy she had sex with when she was 14? Really? She has sex with him again (even though he is married) and then just walks away from him after telling him she never had feelings for anyone else like she had for him. Later she marries Paco even though it seems their relationship was going nowhere early on.
Elizabeth - She is basically a vindictive, manipulative whore for most of the film. She pointlessly has an affair with her neighbor and plants evidence of it in their apartment in an obvious attempt to destroy their marriage even though the woman is with child. Of course we never see what really happens. She seduces her boss for no apparent reason. He offers her a promotion and she turns it down so it wasn't self-interest. She decides to leave him but then of course the near impossible coincidence happens when she is spotted by Paul's daughter through a window. Absurd. That leads me to Paul.
Paul- His immediate, incautious agreement to have an affair with Elizabeth is unrealistic. He was a big time lawyer running a prestigious firm, surely he understood the potential scandal of having an affair with a subordinate young enough to be his daughter. He learns she is carrying his child, he tracks her down, walks into her office and claims he wants to be with her and raise the baby even though he mentions he has someone else waiting in the wings. He leaves without another word. If he truly loved her and the child he would have followed up on the matter. HE would have raised the baby after Watts died on the operating table. Instead he just disappears from the story. Was he not at all curious about what became of her and his child?
Paco - No reason for him to be attracted to Bening, she treats him like crap right off the bat and is basically miserable even after they are together.
Lucy - She was my favorite character until she goes into a tirade towards the end about what a burden the adopted baby is. That seemed to come from nowhere.
Joseph - He suddenly decides to opt out of the situation even though he knew all along his wife couldn't have kids of her own. Another reaction that comes out of nowhere to create some drama for a feeble plot.
Sofia - She would have quit the lousy maid job. It was down to one day per week and Karen treated her horribly, including accusing her and her daughter of theft. She was mainly there because she liked the mother. Once she was gone there was no reason to stay on and take the abuse.