Do you somehow always get your last word corrected by your Finnish teacher when you construct sentences like the following:
Legojen rakentaminen on + [adjective].
Tämä on tosi + [adjective].
Nukkuminen on + [adjective].
It’s often about the partitive, right?
Just in case you're familiar with the term gerund in linguistics... I thought I'd write about something that may help you along the way.
In English, the gerund is the -ing -form (running, singing, playing, etc.). The Finnish equivalent is often, though not always, marked by -minen in the verb construction.
Perhaps this will make it easier to understand why the partitive mysteriously appears when you're describing an activity, like in
Suomen kirjoittaminen on helppoa (Writing Finnish is easy)
Tanssiminen on hauskaa (Dancing is fun)
Opiskelu on mielenkiintoista (Studying is interesting)
So, when you're describing something in Finnish that would be in the gerund form in English, you should usually put the adjective in the partitive singular in Finnish, like in the above sentences!
I hope this helps!