"Never ask people. Not about your work. Don't you know what you want? How can you stand it, not to know?" (1.2.6)
Roark and Keating's early discussion about making decisions really sets up the contrast between the two men. Roark has always been certain and finds it upsetting to not know things.
"Do you always have to have a purpose? Do you always have to be so damn serious? Can't you ever do things without reason, just like everybody else?" (1.7.56)
Roark is logical, with a constant purpose, and Keating is more emotional and has trouble deciding. The two men's differences aren't used for comedic effect, sadly. Instead, Keating is just wrong and miserable and Roark is too cool for school.
He went away, relieved and desolate, cursing himself for the dull, persistent feeling that told him he had missed a chance which would never return [....] (1.12.269)
Keating is scared to make decisions and choices, and it's this character trait that drives his decisions (if you can call his actions "decisions" at all) and actions throughout the whole book.
"Don't you know that most people take most things because that's what's given to them, and they have no opinion whatsoever?" (1.13.110)
The idea of most people's lack of options—and lack of will to choose—is a frequent motif throughout the book, and it's something that both good and bad characters comment on.
"But a desire to choose the hardest might be a confession of weakness in itself." (2.6.116)
This grammatically awkward sentence refers to the oh-so-common tactic of setting yourself up to fail. It's easy to think that the cards are stacked against you when you choose to pursue something that is super-hard.
"And what, incidentally, do you think integrity is? The ability not to pick a watch out of your neighbor's pocket?" (2.10.35)
In context, this is a sly little comment. Integrity, according to Roark, is a positive action. And we don't mean that it's nice; rather that it's something you do.Failing to do something (like not pickpocketing) doesn't fit the Roark definition of integrity.
"I can't live a life torn between that which exists—and you." (2.14.114)
Dominique here says she has to choose between Roark and the world. This is because Roark is the closest thing to an outlaw in the decidedly un-Wild West world of architecture. He sure rails against the constraints of society, though.
She had not noticed him take her hand; it seemed so natural and what she had wanted from the moment of seeing him. But she could not allow herself to want it. (3.7.16)
The ever-neurotic Dominique often refuses to make positive choices for herself. Oddly enough, her insistence on not wanting mirrors Toohey's advice to Katie and Keating, when he tells them not to want things.
"Isn't that a luxury worth achieving? Does it matter how? They were the means. You're the end." (4.2.60)
Gail Wynand gets his Machiavelli on in this quote. The ends justify the means, according to Wynard.
"Your soul has a single basic function—the act of valuing. (4.4.87)
Roark sees souls as decision-making machines. It's interesting he uses the term "valuing" here, since value has a connotation linked to money and commerce.
"It's the hardest thing in the world—to do what we want. And it takes the greatest kind of courage." (4.10.62)
Keating learns a very hard lesson over the course of the book, but in the end he comes to recognize the courage it takes to be an individual and make decisions that go against the crowd.