[T]he addict himself has a special blind spot as far as the progress of his habit is concerned. He generally does not realize that he is getting a habit at all. He says there is no need to get a habit if you are careful and observe a few rules like shooting every other day. Actually, he does not observe these rules, but every extra shot is regarded as exceptional.
William Burroughs, Junky, New York, 1977, p. 22