A Finn here. And just as many other finns, I'm confused to why Finland ranks at the top. Yet, this seems like a case of someone looking to disprove a theory and thus finds the arguments. For example; Health metrics isn't a good measure, considering that Scandinavia has free health care, and this leads to more cases of mental health issues are recorded. Suicides aren't a great metric either, considering that Swedes and Finns have fairly high level of access to guns. I do agree that happiness is a term that is difficult to define, and that "happiness" is a bit misleading. "Content" is a better description.
Also, I think it's easy to misunderstand the Finns from the surface of us. We don't exhibit happiness, and we don't express happiness in a way that is easily observed. Finland ranks at the top of trust in other people, and being one of the least corrupt countries in the world. Those two metrics are a hint into how we Finns relate to other people. Also, it's difficult to get to know Finns, and for this reason it's difficult for outsiders to understand the Finns and the mentality.
On the anecdotal side, earlier this year I solo-traveled the US for 4 weeks, and out of those I got into deeper conversations, I was struck by how sad people were. That made me more convinced that I live a very happy life, in a happy place.
Edit: Some references: Weapons per capita: https://en.wikipedia.org/wiki/Estimated_number_of_civilian_g... Corruption index: https://www.transparency.org/en/cpi/2024 Trust in others: https://www.visualcapitalist.com/mapped-where-people-trust-e...
That fuzzy line that sits between happiness and contentment is worth some exploration. For some the two are one and the same but for others “happiness” represents something closer to a perpetual Disney-movie-good-ending sort of emotional state that I suspect is broadly speaking unrealistic. I wonder how much sadness has stemmed from chasing that unattainable ideal.
"We don't exhibit happiness, and we don't express happiness in a way that is easily observed"
I would far rather live somewhere where people look unhappy but are actually pretty content with life than somewhere where people feel compelled to look happy even though they are actually feeling pretty miserable.
But then again I am an aging Scot so I'm biased. ;-)
Edit: I'm also just back from a visit to Finland.
As a Murrcan greybeard now having lived more than half my life in Finland, I agree with your second-paragraph observations on the people and the mentality.
The level of societal trust here is still very high. I say "still" because methinks Western media and social media serve to erode such things. My 0.01€, YMMV.
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Also regarding "comparison of suicide numbers", in many religious regions suicide is a problem for your soul and therefore a problem for your still-living relatives.
So there is a huge incentive for religious societies to let a family member's suicide appear like an accident. Suicide rates are an extension of mental health disease rates and extremely hard to compare without correcting for many factors.