What does "unfound" do for the theme in "Facing West from California's Shores?

The word “unfound” may be considered as the poem’s major
idea because it summarizes the idea of the search. As a general principle, even if
something is not found—say a cure for a supposedly incurable disease —that lack of
success does not deny that the cure may nevertheless exist somewhere if not here. The
poem’s theme is therefore that one’s search cannot end as long as one is alive, even if
we never reach the destinations we set out for so long ago. This is one of the most
popular poems read on the first day of a class for it is never the destination that
matters but the more adventures of the travel itself which provides all of the
rewards.