What is the main theme of Sherwood Anderson's book Winesburg, Ohio?

The
introductory section to s book titled €“ a section labeled The Book of
the Grotesque €“ lays out many of the key assumptions that underlie  Andersons book as a whole. 
One passage in this introductory section is particularly relevant to the main theme of Andersons
text.  This passage describes an old writer who has a theory that most human beings are
grotesques €“ that is, distorted in some way, so that they never achieve a comprehensive
wholeness. The narrator of the chapter reports that

the
interest in all this lies in the figures that went before the eyes of the writer. They were all
grotesques. All of the men and women the writer had ever known had become grotesques.

The grotesques were not all horrible. Some were amusing, some almost beautiful, and
one, a woman all drawn out of shape, hurt the old man by her grotesqueness.

The old writer works on a book that will depict and explain
examples of the kinds of grotesqueness just described. Andersons own book will function in
much the same way: it will describe various kinds of grotesque people and various kinds of
grotesque behavior. The very idea of grotesqueness implies some healthy norm from which a
grotesque person deviates. A grotesque character is limited and narrow-minded in some
important way and has thus lost the capacity for a richer, deeper, better-balanced life. A
grotesque, Anderson believed, is a person who has embraced one limited truth to the
exclusion of others, thus turning each truth into a falsehood (Winesburg,
Ohio, edited by Malcolm Cowley. New York: Penguin, 1992, p. 24).

A
grotesque person need not live an ugly life. As the passage quoted above makes clear, the old
writer considered some grotesques amusing and some almost beautiful. But almost is the key
word here: a grotesque, almost by definition, cannot achieve true beauty, because true beauty
implies harmony and wholeness, and those are precisely the qualities that grotesque persons
lack.  Winesburg, Ohio is a multifaceted gallery offering the portraits of
many different kinds of grotesques. The great Russian novelist Tolstoy once wrote that Happy
families are all alike; every unhappy family is unhappy in its own way. This quotation might
easily be adapted so that it is applicable to Winesburg, Ohio: whole
persons are all alike, but each grotesque person is grostesque in his or her own way.