Insight and Principle of Sufficient Reason

As has been previously discussed, Insight is cognitive access to a substratum, and to how the stratum is generated out of the substratum.  In other words, it is the basis of an explanation of the Causality of the substratum.  Often, the object of Philosophical Insight is a Principle, e. g. the Water of Thales, the account of which includes an explanation of how what is apparently not Water is derived from Water.  Now, such explanations have not always stood up to scrutiny, prompting the new Insights and new Principles that have constituted the history of Philosophy.  Thus, the object of Philosophical Insight can be generalized from these efforts as a Principle of Sufficient Reason, i. e. a Principle that explains both itself and everything else.  But, with Parmenides, the Philosophical project becomes truncated.  For, he exempts his Principle, The One, from having to either recognize or explain Multiplicity.  The subsequent tradition is not as extreme, generally recognizing Multiplicity, as an inferior realm, but  offering no explanation of why the superior realm generates it.  Notable in this tradition is Schopenhauer, who resuscitates the Principle of Sufficient Reason, only to consign it to the world of Representation, without recognizing that he needs to apply it to his Principle, Will, in order to explain how Representation comes about, regardless of whether or not Representation is real, irreal, or unreal.  As a result, Philosophical Insight is reduced to functioning as a vehicle to presumed Otherworldliness, rather than as determining the nature of the given, as a prelude to modifying it.