Sometimes direct damage by card effect is very substantial, and i was thinking wether or not the character's defence count's?

from another angle you could say if your character has 2 defence and you must deal 1 damage by treachery card effect nothing happens.

I can't wrap my head arround this!

Defense doesn't count.

Defense counts only when you're resolving attacks: in this case, you subtract your defense strength from the attacking strength of your opponent, and in case the result is positive, this number becomes damage.

But when an effect damages someone (one of the characters you control, certainly, but also one of your enemies), this is direct damage, not something that can be absorbed by defense.

Otherwise, cards like Gondorian Spearman would be mostly ineffective, or Thalin's ability would be not so lethal, and so on.