Your summary captures the main theme well, but I can see how the ending might need clarification to emphasize that Buckaroo Bill’s journey, despite not catching the Whopper, remains significant. Here’s a revised version:
The theme of the story centers on the idea that facing seemingly insurmountable challenges with courage can lead to personal triumph, even if external victories are elusive. Fearless cowboy Buckaroo Bill embarks on a daring quest to capture the legendary Whopper of the West, a feat no one has accomplished before. Although he ultimately does not succeed in bringing the creature to shore, his adventure and bravery leave behind a legacy that inspires others, proving that the true victory lies in the journey itself rather than the outcome.
This revision clarifies the message about the importance of the journey and the bravery shown by Buckaroo Bill.