Because it’s long, I have set this video to start at the discussion of sisu; it’s worth watching all the way from the beginning, however.
Sisu has been described by The New York Times as “the word that explains Finland”, and the Finns’ “favorite word” – “the most wonderful of all their words.” During the famous Winter War of 1939–1940, the Finnish perseverance in the face of the invasion by the Soviet Union popularized this word in English for a generation. In what might have been the first use of sisu in the English language, on January 8, 1940, Time Magazine reported:
The Finns have something they call sisu. It is a compound of bravado and bravery, of ferocity and tenacity, of the ability to keep fighting after most people would have quit, and to fight with the will to win. The Finns translate sisu as “the Finnish spirit,” but it is a much more gutful word than that. Last week the Finns gave the world a good example of sisu by carrying the war into Russian territory on one front while on another they withstood merciless attacks by a reinforced Russian Army. In the wilderness that forms most of the Russo-Finnish frontier between Lake Laatokka and the Arctic Ocean, the Finns definitely gained the upper hand.
—Time Magazine, January 8, 1940
This is also sisu:
Translation, according to YouTube commenter CityKanin, 8 months ago:
(remember this tells of the time that Finland was completely depending on agriculture)
Voiceover: The Finnish Guts
Actor: God dammit Devils, not longer shall you rape my lands Frost! That is certain, dammit! God be damned! Hell, this is for sure, dammit!
(He is referring to the frost that comes and kills the crop and cursing it away…)
As is, apparently, this:
(All of the above via SC.)