Actually it is
very possible:
Don Quixote = ~500,000 words
(500,000 multiplied times the number of combinations of same words) times (number letters and punctuation, spaces and numbers)*(combinations of same characters) =
1 chance in a little over 4 quadrillion (4 thousand trillion) that Don Quixote would be spelled out. That is less than infinity.
But I must warn you: this is exponentially far greater than the number of grains of sand on an average beach (512,000,000,000):
http://www.6footsix.com/my_weblog/ho...of-sand-i.html
You could pick up one by one every grain of sand on a typical beach and not find that story.
So to put it in human terms, it is for all practical purposes impossible to find that string of Don Quixote in your brief lifetime. But it exists, theoretically.