Never such a thing as "can't"! But if that's the problem, try just practicing. Don't make an actual game, just a small "visual experience". Like The Mirror Lied--you ever seen that game? It was experimental, and it's short and sweet.
I'm a writer, so my analogy is this--writing a short story and a novel. We all dream of writing novels, but rarely have I met someone who finished one. Most they could go in is five chapters. (And yes, that person described is possibly me.) But if you're capable of writing five chapters, then you're obviously capable of a short story!
I'm just going to theorise for a bit. No idea if this is true for anyone, but it certainly is for me... Thing is, no one here knows what you're capable of yet. Therefore, they don't know if you're going to be dead set on finishing this project.
What dolarmak said here rings true for me. I started a large game for my first project, and it was so big that I had to ask several artists to participate. They did, and happily when they heard of the idea--but the problem is that the game was so big, I eventually couldn't keep up with it. And trust me when I said they were not happy. Among some of them were character artists who made art for up to 10 characters. And that work was wasted because I misjudged my own capabilities.
Spriting and making character graphics, as nice and simple as people sometimes think it is, is hard work. Have you ever tried making your own character graphics? I have--and it kills me. I was never able to come up with something I quite liked as much as other games. This applies to composing music, too. Ask Germany, he's a musician and even though he works hella hard, composing one piece can drain the life out of him. (Although it might just be because composing isn't his repertoire. :P But take it as an example.)
Long story short, work to understand the engine thoroughly! Post some things showing what you're able to do. Eventually people will have faith in your skills and capability and will know you can handle a big project. :) Then perhaps people will help more.
again i don't know if this applies for people here, but it does for me.