They did that smartly.
The rest of WWII continued on for 5 years or thereabouts.
The lesson for everyone ~ the Finland had an army that could beat both the Russians and the Germans. The rest of the world took 5 more years just to beat the Germans.
Irrespect of how folks want to make the war between Russia and Finland look, they must also consider the war between Germany and Finland.
Finland was no one's co-belligerant. On the other hand, in the German war against Poland and the Russian war against Poland, Germany and Russia were co-belligerants.