I just beat the spider boss to get the final heart in Darksiders.  Yesterday, I could not beat her after five tries.  Today on my second attempt, she fell victim to chaoseater.  Darksiders is more than I had expected it to be.  It has an old school feel that I have not seen since (I hate to say it but) Zelda.  What I wanted to know was were there parts of videogames that seemed impossible to beat one moment, but then when you come back to it, you get pass or beat some boss like it was nothing.  Are there any examples you would like to share. 
 
The missile base in COD4 on veteran is probably my roughest moment in gaming.  I stopped  playing  the game for a few months, needless to say I sat down one afternoon, and finished COD4 and I think I only died about 3 or 4 times.  I could not believe it