Sigmund Freud skriver til sin venn Wilhelm Fliess i Berlin (her gjengitt i engelsk oversettelse -- originalen er på tysk):
"Since everyone needs the suggestive influence of someone else in order to obtain a respite from his own criticisms, I have in fact not had anything warm between my lips since then (today it has been three weeks); and today I can already watch others smoke without envying them and even again imagine life and work without this support. It has not been long since I reached this point; moreover, the misery of abstinence has been far greater than I ever imaginedóbut that, of course, is obvious.
It is too distressing for a medical man who spends every hour of the day struggling to gain an understanding of the neuroses not to know whether he is suffering from a logical or a hypochondriacal mild depression."
Freud, S., et al. (1985). The complete letters of Sigmund Freud to Wilhelm Fliess : 1887-1904. Cambridge, Mass, Belknap Press of Harvard University Press.