Hashem doesn't ask of us that which we can't do. The Torah says "Ki karov elecha hadavar me'od", which means "it is very close to you" (i.e that it is not difficult). So why does it feel sometimes so hard? The answer is, these profound words of the Torah are true only when one makes a decision in his mind, once and for always, that this is truly what he wants! In other words, it's not half as much a matter of "will power" as it is simply deciding that this is what you want!