Ever since i saw the movie back in 2003 (i was very young) i couldn't understand what Gandalf meant. Later i also read all Tolkien's books about Middle Earth, Arda etc.. Tolkien did write this exact phrase in the book. It is written precisely:
Gandalf put his hand on Pippin's head. 'There never was much hope,' he answered. 'Just a fool's hope, as I have been told. And when I heard of Cirith Ungol———'.
So what exactly is the meaning?
What i think: Maybe he refers to the futility of life, and the insignificant strives of humans to find meaning and hope? But it's only a fool's errand.
Sure there's room for interpretation, but i want to know if there's somebody who is more informed than me, or understands what exactly is meant here. Thanks.