Man is alone in the world, in ...

Man is alone in the world, in tremendous eternal isolation. He has no object outside himself; lives for nothing else; he is far removed from being the slave of his wishes, of his abilities, of his necessities; he stands far above social ethics; he is alone. Thus he becomes one and all.
 Otto Weininger

Quotes from the same author

In order to depict a man one must understand him, and to understand him one must be like him; in order to portray his psychological activities one must be able to reproduce them in oneself. To understand a man one must have his nature in oneself.
 Otto Weininger
As the mental endowment of a man varies with the organisation of his accumulated experiences, the better endowed he is, the more readily will he be able to remember his whole past, everything that he has ever thought or heard, seen or done, perceived or felt, the more completely in fact will he be able to reproduce his whole life. Universal remembrance of all its experiences, therefore, is the surest, most general, and most easily proved mark of a genius.
 Otto Weininger
I regret that I must so continually use the word genius, as if that should apply only to a caste as well defined from those below as income-tax payers are from the untaxed. The word genius was very probably invented by a man who had small claims on it himself; greater men would have understood better what to be a genius really was, and probably they would have come to see that the word could be applied to most people. Goethe said that perhaps only a genius is able to understand a genius.
 Otto Weininger
Mankind occurs as male or female, as something or nothing. Woman has no share in ontological reality, no relation to the thing-in-itself, which, in the deepest interpretation, is the absolute, is God. Man in his highest form, the genius, has such a relation, and for him the absolute is either the conception of the highest worth of existence, in which case he is a philosopher; or it is the wonderful fairyland of dreams, the kingdom of absolute beauty, and then he is an artist.
 Otto Weininger
The psychical condition of men's minds may be compared with a set of bells close together, and so arranged that in the ordinary man a bell rings only when one beside it sounds, and the vibration lasts only a moment. In the genius, when a bell sounds it vibrates so strongly that it sets in action the whole series, and remains in action throughout life. The latter kind of movement often gives rise to extraordinary conditions and absurd impulses, that may last for weeks together and that form the basis of the supposed kinship of genius with insanity.
 Otto Weininger