True love is rooted in the recognition of the moral and mental qualities of the beloved person, and is equally ready to share pleasures and sorrows and even to make sacrifices. True love shrinks from no dangers or obstacles in the struggle for the undisputed possession of the beloved.
Deeds of daring and heroism lie in its wake. But unless the moral foundation be solid it will lead to crime, and jealousy often mars its beauty.
The love of the feeble-minded is based upon sentimentality, and when unrequited results in suicide.
The sexual functions of man present a very marked influence upon the development and preservation of character. Manliness and self-reliance are not the functions which adorn the impotent onanist.
– from Psychopathia Sexualis, R. Kraft-Ebbing, (12th ed., transl. F.J. Rebman, 1901)