He was so charmless and boring (the lead actor was 43 at the time of filming). The filmmakers want us to believe that someone so cute and charming as Francoise Dorleac (who was 21) would ever want someone so plain and boring??? Its absurd.
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You're forgetting two things.
One, he was a "celebrity" of sorts. There are many celebrities that exist who are charmless and boring off the screen or stage, but the simple fact that they are a celebrity will make them appealing to certain people.
Two, he was a writer (as well as a publisher and lecturer). Yes, you see him do the film intro, but you don't get a chance to read any of his writing. There are many authors who are charmless and boring in person but who write stellar books. Certain people are attractive to the artist/writer and/or their output and will (at least initially) ignore the boring aspects that the person might have.
It was very believable that Nicole was into him.
//It was very believable that Nicole was into him///
I think Nicole, as a lower-class girl, was flattered by the attention of a celebrated intellectual first, but, being naturally clever and with a deep insight, she revealed his moral inadequacy very soon, and finally rejected him.
Listen to your enemy, for God is talking
She's got to be a little "morally inadequate" herself to be OK with the label of the "other woman".
Clear eyes, full hearts, can't lose.
She was not supposed to be a saint, first. Second, the "other woman"s label isn't the only inadequacy one can possess, and not the worst one. :-((
Listen to your enemy, for God is talking
Sure, but I'm just trying to point that this matter here isn't as black-and-white as was initially suggested by your post. The woman herself was perfectly alright with having a sexual affair with a married man and perfectly content with him breaking up with the mother of his children for her (until, of course, she changed her mind).
Clear eyes, full hearts, can't lose.
Too bad that my approach seems to be black-and-white. My point is that the movie is all about the man Lachenay. IMO, Nicole, or her moral limitations, didn't interested Truffault as much as Lachenay's interactions with, and his influences on the people around him.
BTW, Franca did have her own faults as well, as an overbearing and controlling wife.
Listen to your enemy, for God is talking
Not your approach I find black-and-white but rather, your statement about Nicole "revealing the moral inadequacies" in Pierre... which seems to imply that Nicole was some kind of incisive angel and not similarly morally bankrupt... or am I misinterpreting what you're saying?
And although the "center" of our story is Pierre, Nicole's somewhat understated role and ambiguous motivations should not be mistaken as a sign that Truffaut wasn't interested in the character or her place in the larger narrative, IMO. The film is about Pierre and the impact of his actions on his wife and mistress but it's also "about" the wife and mistress and "how" they were impacted (for Franca, the "impact" was the end of a long marriage, culminating with a horrible and humiliating revelation; for Nicole, he offered an initially thrilling, exciting affair, which later ended on an abrupt note... for reasons unclear... thankfully).
Clear eyes, full hearts, can't lose.