At some point in life, all of us get that unexpected call on a Tuesday afternoon that distorts our world and makes everything else irrelevant: There’s been an accident. Or, you need surgery. Or, come home now, he’s dying. We get through that time, somehow, drawing on energy reserves we never knew we had and persevering, despite the exhaustion. There’s no word in English for the specific strength it takes to pull through, but there is a word in Finnish: sisu.

This concept, for Finns, is a key feature of national identity. A study published this week in International Journal of Wellbeing seeks to define sisu in a manner that can be understood by English speakers. “Sisu is a Finnish word that goes back hundreds of years and a quality that Finns hold dear but the phenomenon itself is universal,” Emilia Lahti, author of the study and doctoral student at Aalto University said in a statement.

Lahti surveyed 1,200 people about what sisu means, and analyzed their responses to identify key themes. She found that the word encompasses three major concepts:

• Endurance in times of adversity, and a sense of going beyond preconceived capabilities
• Taking action against the odds and being courageous in the face of challenges
• Harnessing previously unexpressed inner energy

“Respondents rarely mentioned sisu in relation to small daily nuisances,” writes Lahti in her paper. “Rather, it seemed to be reserved for major disruptions, and the most commonly used words referred to significant hardships and stress.”

Though sisu helps people get through difficult times, it was not perceived as an unquestionably positive emotion. In Lahti’s survey, she found that people associated it with three main negative effects: Poor mental health, an inability to empathize with others’ suffering, and not knowing when to step back and quit. “If the person has very unrealistic assumptions of mental or physical reserves, too much sisu can lead to foolhardiness and a backlash. Overtaxing mental reserves may cause mental trauma, foolhardiness in the physical domain can even cause death,” wrote one respondent.

Sisu is a fascinating and nuanced concept for many reasons. It conceives of fortitude as partly embodied, rather than purely mental, and it shows our ability to go beyond expectations while also highlighting the deep impact of difficult circumstances. Courage, strength, and perseverance do not quite capture the meaning: The word speaks to human power while acknowledging the limits we must transcend.

Developing the language of psychology can help us understand our own minds, writes Lahti in her paper: “What is it that keeps our lights burning and hearts hoping during the dark night of the soul,” she asks. Sisu captures some of the answer, even for those of us who do not have a direct translation.