For me its when I get an idea of a new deck... then spend hours or days to find all the runes for it, then try it out... and find out it rocks. And especially if its something new unexpected, so it can beat sometimes top players who get upset. Its what can get me sucked back to the game for days or weeks or more. Usually the first days/week of this deck, before everyone starts to include counters or copy it etc is the most fun. This is very special with poxnora and can get you so addicted.
What I try to say is something like this: The wins, especially the extraordinary ones after some thinking and building, give much much more game KARMA than any losses can ever take away. So understand, don't shape the game from what the top 50-100 rankers say, they don't want to lose to keep their ranks. But they must lose sometimes to lower rankers if they want the game to exist, if they want new players to stay.