Brief Encounter and Adultery's Failure to Make Sense

Eve Tushnet has this to say about David Lean's Brief Encounter (1945):

The lead actress, Celia Johnson, is pretty excellent, although to be honest all she's asked to do is stare at the camera with a look of repressed misery. But I loved her huge-eyed, oddly lumpy and jawy face. She looked raw.

None of the other actors struck me at all, though the final scene was very poignant.

My main problem, watching the movie, I think was a culture-clash problem. I was strongly reminded of the Chris Ware line from Jimmy Corrigan: The Smartest Boy on Earth—

But with the inevitable forward march of progress
come new ways of hiding things,
and new things to hide.

Because we lie to ourselves differently now, it was easy to feel that the narrator of Brief Encounter was being willful and stupid to a degree and in a way which I found totally unsympathetic. Her self-deception tricks felt alien to me, and so it was hard to feel like I was implicated in her actions.

Eve is right that adultery depends upon self-deception of one kind or another; my question, then, is: what is the truth behind the self-deception?

Let's ask the director, in the person of his representative Anthony Lane:

[David] Lean was one of two sons born to Quaker parents of Cornish stock. His father, Francis (better known as Frank), was an absurdly handsome accountant, unlikely though it sounds. David’s mother, Helena, came from a family of “artists, inventors, and engineers,” as he later described them to Kevin Brownlow, whose 1996 biography remains the best and most exhaustive account we have. Lean himself described his mother as “sweet and very pretty,” although Brownlow spoke to two of his cousins, who claimed that their aunt Helena had been a woman of fury: “She had such an awful temper, it’s no wonder Frank couldn’t live with her.”

The couple split apart; Frank fell in love with somebody else, and David, then fifteen, was left with his mother to pick up the pieces. The angry wife had dwindled into a weeper: “She used to spend her time crying and to this day I cannot abide tears. If my wife starts to cry, I say, ‘Stop crying!’ in a brutal way, because it reminds me of my mother. I spent my life with tears.”

We're dealing with the product of a broken home, which means that Lean can be relied upon to understand that, sometimes, the opposite of divorce is adultery. On the other hand, we have a man who "cannot abide tears," which means that for him an affair, if it is to save a marriage, must be undertaken in a spirit of calculating pragmatism in order to preserve everyone's dry-eyed emotional discipline. If the affair turns into an adventure in boundless passion, we're back to tears again; more unbridled emotion, more women who can't stop weeping.

And that's the paradox of adultery as Lean imagines it: Affairs are only good if we're sensible about them, but, if we were entirely sensible, we would realize the folly of having affairs at all. Brief Encounter is an anti-cheating manifesto, not because of any deontological rule against cheating, but because Lean doesn't think that adultery makes sense. (Divorce, on the other hand . . .)