Boyhood (2014)
For 12 years, Richard Linklater gathered his actors to capture the real coming-of-age of the protagonist—from a child to a college student. The film had no strict script: each year, Linklater, Ethan Hawke, Patricia Arquette, and the young Ellar Coltrane discussed what was happening in their lives and turned it into scenes.The film "Boyhood" became the decade's main experiment in narrative cinema and a subject of study in cinematography programs.
We've seen people grow up in various films and TV series. But we've never seen it happen in such a short span of screen time. That's what makes 'Boyhood' unique. There is no other work that can be directly compared to it., notes the renowned critic Roger Ebert.

Source:
imdb.com
The Thief and the Cobbler (1993)
Richard Williams began working on this animated film in 1964, drawing inspiration from Eastern tales and Persian miniatures. However, the creation progressed slowly: the director simultaneously shot commercials and worked on animation for major films such as "Who Framed Roger Rabbit."In 15 years, the animator completed only 15 minutes of material. When Warner Bros. joined the project in 1990, the pace quickened. But Williams, as Indiewire reminds us, was a terrible perfectionist, constantly exceeding budgets and deadlines. As a result, the studio took the project away from him.
The film was released without the author's involvement, reducing his vision to the standard format of a children's cartoon. The original director's cut—already a symbol of creative perfectionism—was shown to the public by Williams only 51 years after the start of the work.

Source:
imdb.com
The Evil Within (2017)
Andrew Getty, heir to an oil empire, decided to spend his millions on the horror film "The Evil Within"—his first and only movie. He wrote the screenplay himself, based on his own nightmares, and used his mansion as the filming location.The director began in 2002, but the filming progressed in fits and starts and gradually descended into chaos due to Getty's inexperience. As the work continued, money ran out, problems accumulated, and actors left (and even died). However, Andrew, driven by mad ambitions, did not abandon his creation. Listen closely, and you can hear him muttering off-screen:
It's okay, we'll fix it later.
13 years later, Getty died without seeing the premiere—the film was completed by another team. Today, "The Evil Within" is called the strangest horror of the decade, and it's true: the director's paranoia and obsession are felt in every frame.

Source:
imdb.com
Kill It and Leave the City (2020)
14 years of personal therapy — this is how director Mariusz Wilczynski describes his animated work. Initially, it was a short film, but after the death of close people, Wilczynski decided to turn it into a full-length confession.Each horror scene was created by hand, and through surreal images, the director communicated with those who were no longer there.
In a short time, people who were important to me passed away. I didn't have time to say goodbye to them, I do it through my animation, quotes the Polish film magazine Ekrany.

Source:
imdb.com
Blood Tea and Red String (2006)
It took 13 years to create this stop-motion film. The reason? Director Christiane Cegavske worked on it almost single-handedly, crafting each scene manually.Making a puppet, building the set, completing a scene; each of these actions is a small triumph, shares Cegavske.
Her efforts paid off. Viewers noted that it was the long and meticulous work that gave the cartoon its mesmerizing aesthetic. On Rotten Tomatoes, the "fairy tale for adults" received a 92% approval rating, and critics called it
a genuine work of outsider art.

Source:
imdb.com
Why is Yellow the Middle of the Rainbow? (1994)
This is not just a documentary; it's a family chronicle spanning 14 years. Director Kidlat Tahimik filmed his family's life in the Philippines from 1980 to 1994 — through their personal events, the country's history was captured.This film is a rare example of home footage becoming part of world cinema. It's also a reminder that a sincere author's perspective can sometimes be far more valuable than big budgets. It's no wonder critic Christopher Pavsek said:
There are indeed few films like this, if there are any at all....

Source:
spikeisland.org.uk
Coffee and Cigarettes (2003)
The most laid-back long-term project on this list. Jim Jarmusch started working on "Coffee and Cigarettes" in 1986 and completed the project 18 years later. It all began with a short film, and then the director gradually added new episodes featuring iconic artists like Iggy Pop and Roberto Benigni.Each vignette is a conversation at a table, but together they form a portrait of a generation. "Jarmusch managed to assemble as diverse a cast as you could ever see. The episode where rappers GZA, RZA, and Bill Murray intellectually discuss smoker's cough and herbal remedies can captivate even the staunchest skeptic of such works," writes a user on the IMDb platform.

Source:
imdb.com