"I think we're going to the moon because it's in the nature of the human being to face challenges. It's by the nature of his deep inner soul... we're required to do these things just as salmon swim upstream"

The quote recommends that human beings have a fundamental drive to take on challenges, to explore, and to reach new heights. Simply as salmon swim upstream, human beings are forced to face challenging accomplishments such as going to the moon. The desire to push limits and push the limitations of what is possible is woven into the fabric of humanity.