It's a funny contrast, though not an unfitting one. Mamoru is so accustomed to structure, direction and clarity of objectives. It's hard to envision this wait-and-see approach Goku seems to be taking. It's so easygoing (like Goku himself, or at least what Mamoru remembers of him).

"That sounds relaxing. I hope you find something interesting without trouble-- and that it doesn't turn out to be trouble itself."

It's an easy destination for the young and aimless.