Another litvish illustration:
Matzah, is called lechem oni. Is this a din in sipur yetzius mitzraim (telling the story of yetzias mitzraim) or matzah? If it is a din in matzah, then we are not yotzei if the matzah is not left open on the table but otherwise not every matzah must be on the table just that we should tell it on any matzah.