It is not a rule, it is unwritten - but I could guess various reasons why it has developed as a component of Finnish society. It is most visible in smaller town societies - say 20 - 80,000. In the Finnish metropolii my guess would be a smaller per capita social investment. Remote, purely agricultural societies rarely reach critical social mass - though the church may still play a community role in these.

So this altriuism seems to fbetter lourish in certain sized communities. I assume that neighbourhoods can act as a flocks.

You can't be me, I'm taken