What does the statement, "We do not ride on the railroad; it rides upon us," mean?

We
have to pay to ride on the railroad. In order to be able to pay, we have to work to earn the
money. So although we seem to be traveling in fast and without effort we do not take into
consideration the amount of labor we had to put in to pay for the train ticket. In Thoreau's
opinion it would be better to walk to wherever we are going, and probably better still not to go
very far at all. His friend Emerson said, "Travel is a fool's paradise." Thoreau
wrote: "I have traveled quite extensively, in Concord." He didn't believe you had to
travel very far to see interesting and beautiful sights....