If I am trying to find a work of literature (poetry, short stories,
novels) that has been published (and I do not know the author or the
work) can I just type in any 3 or more words and put quotation marks
around them to find out the title and author. Sometimes i do this and
it seems to work and other times it does not work? Why the
inconsistency?

One can only find on the 'net what is actually catalogued on the 'net
- which is to say that if the text of the author that you are
searching for is not somewhere on a page in that exact phrasing, it
will not turn up in any search.

Many published works are not online for obvious reasons (not public
domain); however, even when they are mentioned and reviewed online, it
is not a sure thing that the particular passage or words you chose are
going to be excerpted.  Also confounding the issue is that the three
words you choose may well be part of some other work that includes
those three words, thus returning many links not germane to the
search.