Tirin looked at them, derisive. “You’re all crazy. Who wants to actually get locked into a place like that? What for?” Making the prison had been his idea, and it sufficed him; he never realized that imagination does not suffice some people, they must get into the cell, they must try to open the unopenable door.
It is a scene from Shevek's teenage years when his peers and him study about Odo's time in prison. Excited about this new concept, the boys want to experiment with it themselves. From the lines we can see that it was Tirin's ides to recreate it. Later in his life we discover that his artistic mind had no place on Anarres and it drove him insane out of fear to be abandoned by the society. This scene leads to one of the boys spending quite a long time in their makeshift prison, and their realization of what that sort of thing does to a person.
Paradise is for those who make Paradise. He did not belong. He was a frontiersman, one of a breed who had denied their past, their history.
His entire life Shevek has a feeling of not belonging to his society, to the Anarres Paradise. The more he learns about it the more he realizes the denial that the people live in when it comes to their past. In accordance with his theory, the time moves in a cycle and there is no moving forward without facing that past, which he eventually decides to do in his solitary voyage to Urras.
He went to some, because he had come to Urras on a mission and must try to fulfill it: he must urge the idea of brotherhood, he must represent, in his own person, a solidarity of the Two Worlds. He spoke, and people listened to him and said, “How true.”
Shevek came with honest motives to Urras, he came to face his history and bring the two worlds closer, to show the beauty of a life where people live as brothers instead of enemies. This was before Shevek realized the truth of the warm welcome he received there, which is to give them what they need to gain power, which is his theory of Simultaneity. This bland answer of "how true" represents how little they care for what he has to say, how disinterested they are in this talk of brotherhood.
