Why is it hard to see the value in making a product that competes in an existing profitable and developed market space, but does so better/cheaper/more conveniently? Isn't that a significant portion of the startups in YC? E.G. Hipmunk - simply a more user friendly flight search and hotel booking? Mariusz shouldn't have to spell it out for YC in this case.
If the issue is as Mariusz describes, he shouldn't be blaming himself, but rather YC instead for not seeing the obvious market potential in fairer pricing. Either YC missed something obvious or the reason YC turned Mariusz down was for a different reason than stated.