ever.

From the nature of the impediment--lack of co-ordination between
the brain and the organs of speech--stammering cannot be outgrown
--no more so than the desire to eat or to talk or to sleep.

Back of that statement, there is a very sound scientific reason
that explains why stammering cannot be outgrown. Stammering is
destructive. It tears down but cannot build up. Every time the
stammerer attempts to speak and fails, the failure tears out a
certain amount of his power-of-will. And since it is impossible
for him to speak fluently except on rare occasions, this loss of
will-power and confidence takes place every time he attempts to
speak, so that with each successive failure, his power to speak
correctly becomes steadily lessened. The case of a stammerer might
be compared to a road in which a deep rut has been worn. Each time
a wagon passes through this rut, it becomes deeper. The stammerer
has no more chance of outgrowing his trouble than the road has of
outgrowing the rut.

Dr. Alexander Melville Bell recognizes the absolute certainty of
the progress of stammering and the impossibility of outgrowing the
difficulty, when he states in his work, PRINCIPLES OF SPEECH (page
234):

"If the stammerer or stutterer were brought under treatment before
the spasmodic habit became established, his cure would be much
easier than after the malady has become rooted in his muscular and
nervous system."