Nothing prepares you for the shock that is the Cannes film festival: the adrenaline, the fatigue, the elation and the emotion, but also the hunger, the anger, the magic and the ridicule. For young cinephiles, and for almost everybody who works in the film industry, it is the mecca of cinema and has been so for nearly eight decades. Anyone going for the first time this week, as I did 25 years ago, should not listen to the old grognards – Cannes’ battle-worn veterans – who will lament that the festival has become an abominable circus and swear this year will be their last. It is a circus, and you can bet they will be back for as long as their knees can take it. For there is nothing quite like it.

Born to counteract Benito Mussolini’s Venice film festival, its first edition was planned for September 1939, but Adolf Hitler had other plans. The previous year, under pressure from Berlin and Rome, the Venice film festival’s top prize, the Coppa Mussolini, was handed to Leni Riefenstahl’s propaganda film Olympia, prompting the French, British and American delegates to walk out. Hence Cannes, conceived as the festival of the “free world”. More than 80 years later, for all its sins, it has remained faithful to that founding promise.

Over the decades, Cannes has mutated into an ever-hungrier mammoth, needing more space, and more venues, as it attracts an increasing number of journalists and professionals. A purpose-built Palais des Festivals had to be erected in the 1980s. “The bunker”, as we have come to call it, is not exactly beautiful but brutally efficient at managing Cannes’ mind-boggling crowds. This year, about 40,000 accredited festival-goers are descending on the French Riviera from 140 different countries, with dozens of films selected across all sidebars. At the same time, the Marché du Film, running alongside the festival since the late 1960s, is gathering about 16,000 participants, with thousands of films and projects up for sale. Cannes is both a summit for the cinema elite and a giant film bazaar. When I first arrived as a young critic in my early 20s, it already felt like the centre of a small, overheated world.

For 11 days in May, three different worlds lead parallel lives – critics, deal‑makers and red‑carpet royalty – colliding almost by accident on the seafront boulevard known as La Croisette. Hundreds of critics watch multiple films a day with monastic discipline. When they give in to parties, they bitterly regret it the next morning. You can spot some of us sleeping through entire screenings; how some colleagues manage to review films is a mystery. I remember a well-known French critic who had such vivid dreams in the darkness that he became convinced they were scenes in the films. His reviews were full of brilliant analysis of moments that did not exist.

We critics rush between screenings, press conferences, interviews, our desks and the bunker’s free espresso machines, often forgetting to eat or even pee. Downstairs, in the bunker’s basement, and in hotel suites and rented apartments, the film market runs day and night: buyers juggle numbers, producers charm, directors and screenwriters fight for their vision. Above them floats Cannes’ top layer – stars and “talent” spending hours in hair and makeup before climbing the 24 steps of the red carpet in borrowed couture and jewellery. When people in the industry groan, “oh God, it’s Cannes again”, it is this collision of financial anxiety, choreographed glamour and sheer exhaustion they are bracing themselves for.

These worlds sometimes collide in the most poetic or grotesque ways. One morning, rushing to my first screening at 7.30am, I was walking along the Croisette when I saw, coming towards me, slightly dishevelled in a tuxedo, Jack Nicholson on his way back to his hotel after a long night. I smiled, he smiled back. He was alone, no bodyguards, no chaperones. Those were the days. I also shared a lift with Takeshi Kitano in full samurai attire, and I will never forget turning into a hotel corridor and finding myself nose to nose with Max von Sydow – Ingmar Bergman’s medieval knight from The Seventh Seal. My cinephile heart skipped a beat.

One of my favourite sidebars in Cannes, alongside the competition where you watch the year’s best crop of films, is Cannes Classics, showing restored world masterpieces and documentaries about cinema. I always start the festival there: it is the best way to reset and begin afresh. Then I am ready for the 10-day onslaught of motion pictures, and for the magic moment that precedes each Cannes screening – the festival’s own jingle, a palm ascending the red carpet from underwater and then into the sky, lifted by the ethereal arpeggios of Camille Saint-Saëns’s Carnival of the Animals.

In 1955, Cannes gave its first official Palme d’Or to Delbert Mann’s Marty; half a century later I found myself befriending its wonderful star, Betsy Blair, on the Croisette. I had the joy of seeing Ken Loach twice climbing those steps to collect the Palme, escorted by police outriders from Nice airport as if he were a head of state. I watched Iranian directors Jafar Panahi and Mohammad Rasoulof showing films at peril to their lives. For all the craziness of the red carpet and the samurai outfits, Cannes never forgets that it was founded as a gesture of resistance. That, as much as the glamour and the exhaustion, is why we keep going back.

• Agnès Poirier is a political commentator, writer and critic for the British, American and European press