For over seventy years, following the signing an Agreement of Friendship, Cooperation and Mutual Assistance with the USSR in Paris in 1948, Russia and Finland have shared a long border, and a long history, with no resentment or difficulties, each side scrupulously adhering to the arrangement, which was signed in perpetuity. They may not have been bosom neighbours, but neither neighbour annoyed the other by playing rap music or holding loud parties at two o'clock in the morning, and they rubbed along OK.
Although the USSR, now the Russian Federation, has never shown any antagonism or threat to Finland since this agreement, Finland felt that Russia's actions against totally different countries for unwelcome but rational reasons were somehow a threat to itself. Basically Finland seems to have understood little about Russia or international geopolitics..
This paranoia made no sense, and I said so at the time, and so did a fair minority of Finns. Unfortunately a callow, inexperienced young PM thought otherwise, and with public support, applied to become members of NATO.
The stupidity of this decision should be obvious to anyone with any sense of reality. So the previously harmless little deer on the edge of the big bear's forest arms itself with a rifle, and the big bear looks on, and says, "what are you doing, little deer? There used to be plenty of space for both of us, and now you threaten me with a gun? Watch out little deer, I can make your life a bit harder in many ways you haven't even thought of yet"
So Russia now starts creating a nuisance of itself to Finland. Surprise surprise. Presently it's escorting migrants and refugees to the Finnish border. Cruel on the migrants, in the snow and minus 20 deg C temps, but bears can be cruel. This is just the start, it'll be a slow trickle of mischief. It won't make Finland any friendlier to Russia, of course, and maybe just confirm in the collective Finnish mind that you can't trust Russia, but why would Russia care now? That this little country prefers to play with the big hunter from over the seas and join forces with Russia's mortal enemy - that's just the way things are, says Russia, we'll deal with it in whatever way we need to. Indeed, if we ever have a war with NATO, it makes life a bit easier, we'll know which country to invade and destroy first.