Frustrating Boss Battles in Games

I was playing gears of war 3 today on hardcore, and for over an hour I was stuck on the same stinking boss. Now, I'm not the best player of games out there. I'm not in the MLG, nor could I even come close to competing with probably their worse players. I am, however, quite an experienced gamer. I've been gaming since I was all but 5 years old when my grandma bought my family a Sega Genesis with the Lion King. 
 
When that boss battle came up today though, It royally kicked my butt...over...and over...and over again. How frustrating is that!? We've all been there, and we all know how irritating it can be when you've got a great flow going with a game, and then boom! A boss stops you dead in your tracks. It's not a good feeling one bit.