To "shoot the moon" or "shoot for the moon" is to go for broke, to put all your efforts into doing something, so that if you fail it is not for lack of trying. As someone mentioned about Hearts - when you shoot the moon it is all or nothing. You either take all the point cards & win big, or you take almost all the point cards & lose big. Maybe in this context it means "good luck with going all out & doing your best - it won't be enough".
To "shoot the moon" or "shoot for the moon" is to go for broke, to put all your efforts into doing something, so that if you fail it is not for lack of trying. As someone mentioned about Hearts - when you shoot the moon it is all or nothing. You either take all the point cards & win big, or you take almost all the point cards & lose big. Maybe in this context it means "good luck with going all out & doing your best - it won't be enough".