Schopenhauer on the Connection between Genius and Madness

From part thirty-six of Schopenhauer's The World as Will and Representation:

The fact that violent mental suffering or unexpected and terrible events are frequently the cause of madness, I explain as follows. Every such suffering is as an actual event always confined to the present; hence it is only transitory, and to that extent is never excessively heavy. It becomes insufferably great only in so far as it is a lasting pain, but as such it is again only a thought, and therefore resides in the memory. Now if such a sorrow, such painful knowledge or reflection, is so harrowing that it becomes positively unbearable, and the individual would succumb to it, then nature, alarmed in this way, seizes on madness as the last means of saving life. The mind, tormented so greatly, destroys, as it were, the thread of its memory, fills up the gaps with fictions, and thus seeks refuge in madness from the mental suffering that exceeds its strength, just as a limb affected by mortification is cut off and replaced with a wooden one. As examples, we may consider the raving Ajax, King Lear and Ophelia; for the creations of the genuine genius, to which alone we can here refer, as being generally known, are equal in truth to real persons; moreover, frequent actual experience in this respect shows the same thing. A faint analogy of this kind of transition from pain to madness is to be found in the way in which we all frequently try, as it were mechanically, to banish a tormenting memory that suddenly occurs to us be some loud exclamation or movement, to turn ourselves from it, to distract ourselves by force.

Now, from what we have stated, we see that the madman correctly knows the individual present as well as many particulars of the past, but that he fails to recognise the connexion, the relations and therefore goes astray and talks nonsense. Just this is his point of contact with the genius; for he too leaves out of sight knowledge of the connexion of things, as he neglects that knowledge of relations which is knowledge according to the principle of sufficient reason, in order to see in things only their Ideas, and to try to grasp their real inner nature which expresses itself to perception, in regard to one thing represents its whole species, and hence, as Goethe says, one case is valid for a thousand. The individual object of his contemplation, or the present which he apprehends with excessive vividness, appears in so strong a light that the remaining links of the chain, so to speak, to which they belong, withdraw into obscurity, and this gives us the phenomena that have long been recognised as akin to those of madness. That which exists in the actual individual thing, only imperfectly and weakened by modification, is enhanced to perfection, to the Idea of it, by the method of contemplation used by the genius. Therefore he everywhere sees extremes, and on this account his own actions tend to extremes. He does not know how to strike the mean; he lacks cool-headedness, and the result is as we have said. He knows the Ideas perfectly, but not the individuals. Therefore it has been observed that a poet may know man profoundly and thoroughly, but men very badly; he is easily duped, and is a plaything in the hands of the cunning and crafty.