Christmas isn’t a national holiday in Japan– less than one percent of the population is Christian . But, because of what is possibly one of the most successful marketing campaigns of all time, for the last 40 years the Japanese have celebrated Jesus’s big day with a big bucket of KFC.

Party Barrel from 1985

Legend has it that the strange pairing started in the winter of 1974 after a non-Japanese customer complained that she couldn’t get turkey for the holiday. “I just have no choice but celebrating Christmas with KFC chicken,” she said, according to KFC.

Having only opened in Japan about four years earlier, KFC was looking for ways to get the Japanese to embrace fried chicken, which is considered more of a luxury product in the country. Christmas might not be a religious celebration in Japan, but the holiday has turned into a commercial affair, with lots of money spent on decorations, gifts, and celebrations. Marrying a special-occasion food with a special occasion made perfect sense, and that year, KFC held its first Christmas campaign: “Kurisumasu ni wa kentakkii!” (Kentucky for Christmas!), advertising a chicken bucket and bottle of wine combo for the equivalent of $10.

Every year since, KFC has run the promotion. But the trend really took off with the 1985 launch of the Christmas Party Bucket, pictured above. KFC created a three-layer bucket to hold, chicken, salad, and ice cream, keeping each item at its respective appropriate temperature: “With this Christmas Party Bucket alone, you can hold a luxurious party,” read the tagline.

Because of the bucket promotion, KFC sales are 50% higher in December than the rest of the year. People line up around the block at the fast-food chain to get a Christmas bucket of fried delights. KFC also takes orders up to two months in advance.

The custom took off, surmises KFC, because:

Colonel’s policy to serve people to let them happy from the bottom of their heart has something very common with our traditional Japanese spirit called ‘Omotenashi’, or spirit of hospitality. In addition, Japanese love Colonel’s mentality to make efforts humbly, tenaciously, and continuously, without giving up. And we have passed down the exact same Colonel’s recipe for so many years to today’s customers.

That seems a bit deeper than reality. It has more likely endured the last four decades because of tradition and nostalgia. The impulse might seem strange and a bit silly to Americans, but there’s not much logic in mall Santas or kissing under a mistletoe, either. “I watch the commercials for KFC and that makes me want to eat chicken,” Satsuki Sakamoto, a 22-year-old-college student in Tokyo told The Diplomat, an Asia-Pacific news outlet. “I have this image that Americans eat chicken for Christmas.”