Slightly, it is only knowing that one does not know the other, and the expression is a "semi-understood" state. Half can be seen, half can't be seen clearly. In visual performance, it is to make entry points on "visual weight". You can see "omitted" or "know". Since "omitted" is used as a clear expression, "knowledge" is used as a weak expression, but what is known is rather a seemingly absent. It is to emphasize a point of view. Those observation points that are ignored by ordinary people are the problems we need to think about and think about problems from another dimension. The omission is known, and the seek is unknown.