The word is also frequently used to explain Finland’s sporting achievements and feats of physical endurance. Veikka Gustafsson became a national symbol of sisu in the 1990s, when he became the first Finn to climb Mount Everest in 1993. By 2009 he had climbed all 14 of the world’s 8,000m peaks (eight-thousanders, as they are called) without supplementary oxygen. This made him the ninth climber in the world to have achieved this. He also climbed peaks in Antarctica, naming one of them ‘Mount Sisu’.

Gustaffson not only named a mountain after Sisu; his five-year-old son is also called Sisu, and for a while (not any more) he became the face of a popular Finnish sweet called “sisu pastils”.

Having become the embodiment of sisu, who does Gustaffson admire as having sisu? “If I think of the Sherpa people in Nepal, they have lots and lots of sisu. And I think the Balti people who were helping us in the expeditions in Pakistan. They also have lots and lots of sisu,” he says.

For all the sweetness of sisu pastils, sisu has its downsides. Even Gustafsson admits that Finnish sisu also denotes an element of stubbornness, “I do my own thing. If you have sisu, you don’t just endure adversity but you endure what Emilia Lahti calls ‘silent relentlessness’,” he says.

Sisu can also make it difficult to admit weakness. “It’s hard to ask for help. You risk losing face if you admit weakness. That’s a challenge in a culture that holds sisu in high reverence’, Emilia Lahti tells me. If you persevere for too long, results could be damaging. “You might end with burnout if you try too hard.” You can also cause harm to others with too much sisu, she warns. “It’s almost too easy to impose this merciless attitude on other people as well. And it’s very hard to be around people like that.”