I don't know if it's a Finnish tradition only, but a lot of people (around 14% of population in 2010) stop drinking for the month of January. For some it's a way of giving a break for their livers, and some want to see if they are still able to completely stop drinking.

The good thing is having one month per year where it's almost socially acceptable to not drink any alcohol. Of course everyone could just drink moderately all year, but that doesn't seem to happen.