even the most adventurous human adventures in history have been measured in months, we've never displayed the will to commit to years for what would be a token mission.

It's laughable how wrong this statement is. Someone else already posted about Magellan and Lewis & Clark, but there are SO MANY more examples in history. An expedition taking several years was the standard for centuries. One measured in months would have been considered pretty short until around the mid 20th century.