I think, to be totally honest, that to be really submissive, rather than just 'acting it', somewhere inside you there has to be a little 'nugget' of true submissive / non-pushyness so that in certain circumstances you already indentify with the submissive side of the situation.

And because of that 'auto-indentification', it feels natural. Yes, I agree maybe, the submissiveness can be 'honed' to a 'fine edge' but that inital desire / strong association with the role of submissive also has to be there.