When you are dreaming, no matter how hard you try to achieve a correct view of reality, you cannot do so due to the nature of the dream reality. On that level, the dream content is real to you, and the only way you can tell that it is a dream is to simply awaken. I am suggesting to you that even when we 'awaken' to the next level, which is called Waking Sleep, because it only seems that we are awake, but in truth, are still just asleep but on a higher level than that of the dream-sleep state. For all practical purposes, we think ourselves truly awake, and go about employing the rational logical mind in a serious effort to discern reality from illusion, not realizing we are immersed in illusion itself, and that the only way to make such a discernment is to awaken once again to a yet higher level of reality, one which shows you beyond a shadow of any doubt that you are truly awake. The problem is the self, which itself is an illusory entity, and which must be overcome if one is to gain a foothold on higher ground. Otherwise, it will keep you locked into Identification, keeping us asleep while thinking ourselves awake, and thinking itself real, when in fact, it is a fiction we act out in the drama of the 'reality' of Waking Sleep.
The only way that the prisoners in Plato's Cave can realize that the dancing shadows on the cave walls are illusions, is for them to escape to the outside of the cave and behold the glorious Sun for the very first time. Any efforts they make to discern reality from illusion via the dancing shadows on the cave walls will fail. They may even construct systems of thought called Science, Religion, and Metaphysics in order to do so, but these will all pale in comparison to the Ultimate Reality represented by The Sun.