I suspect that a lot of people of my generation have become somewhat inured to the consistent fallibility of sequels. Our experience over the past few decades, whether you’re talking about long-delayed sophomore albums, movie trilogy prequels or Tiny Toons-style presidencies has shown us that franchise extensions lead to almost certain disappointment.

That’s why Richard Linklater, Julie Delpy and Ethan Hawke’s follow-ups to 1995’s “Before Sunrise,” are so remarkable. Each installment has enriched its predecessors, rather than diminishing them. What began almost twenty years ago as an unexpectedly charming flight of fancy between two lovestruck twenty-somethings has blossomed into the quietest, loveliest kind of epic trilogy ever imagined. It’s a series of acutely human, almost mundane conversations played across decades that somehow manage to brilliantly illuminate the arc of adulthood at the end of the 20th and beginning of the 21st Centuries.

That there is a third installment at all — in theaters now — is brazen; 2004’s “Before Sunset” was a nearly flawless bit of storytelling that ended with a thrilling, satisfyingly ambiguous fade-to-black that seemed like an impossible act to follow.

But this year’s “Before Midnight” is richer still, if less perfect. It turns a corner in the story of these two characters whose meet-cute lasted an unnaturally long ten years; their preoccupations are no longer the transcendent ideals of young love, but the quotidian hurdles of being older, raising kids, getting through life. The exchanges between Hawke and Delpy’s characters are still riveting, but also more explosive and more forlorn now. An undercurrent of bitterness runs through it all, borne from the burdens of accommodating loved ones and their ineluctable foibles for years. The first two movies were about ideas of adulthood, and how difficult it can be to aspire to them; this one is about being adults, and how paltry the upsides can be. If that sounds grim, rest assured: it’s an unremittingly talky movie, but the dialogue is still repartee, still frequently hilarious.

The best part of “Before Midnight,” though, is that it affords us the opportunity to visit again with these two amazingly imperfect characters given life by Ethan Hawke and Julie Delpy, to enjoy their company for another hundred minutes or so, and to discover new things that deepen our love for them. This movie gives us exactly what most sequels never do: the chance to burnish our original affections not just through repetition of the familiar, but through challenging our ideas of them, and of ourselves.

At this point, it would be hard to argue that this series is anything less than a cultural landmark. Rarely have we seen fictional constructs grow and evolve over so tremendous an arc of real time, and with so much verisimilitude. These movies have unexpectedly become important works of art. But they’ve also become incredibly intimate for those of us who have followed along, who have grown up alongside them. I have to admit there’s a swelling in my chest every time I see these characters on the screen. They’re like good friends who visit only every once in a while. I can’t wait for the next time.