I get that way sometimes with games too. Just, sometimes when it comes to platforming games, an "easy" puzzle or section for someone is hard for me. Maybe you can chalk it up to not quite knowing the nuiances of the game yet.
Either way, you're bound to have that "Ninja Gaiden Moment," which I experienced along with probably some others. You'll just be pitiful at the game . . . but then all of a sudden things will click. You don't know how it did, but now you're just ninja-flipping through the stages and wiping every enemy out with relative ease.
So, keep at it. And, really, maybe it also might not be the sort of game that you're into. I can't, for the life of me, compete in any level in any RTS game. I just stink. Had a horrific online record of C&C Generals. Terrible at Warcraft 3. Couldn't even beat some of the offline missions. So you never know. Once it becomes not fun, then stop. But if you're having fun with it still, keep at it, and that moment should arrive when you click with the game . . . hopefully