In the Atlas Shrugged introduction, Peikoff quotes Rand’s writing notes, from 1946, about Dagny. I think this is particularly important.

Her error—and the cause of her refusal to join the strike—is over-optimism and over-confidence (particularly this last). Over-optimism—in that she thinks men are better than they are, she doesn’t really understand them and is generous about it.

Over-confidence—in that she thinks she can do more than an individual actually can. She thinks she can run a railroad (or the world) single-handed, she can make people do what she wants or needs, what is right, by the sheer force of her own talent; not by forcing them, of course, not by enslaving them and giving orders—but by the sheer over-abundance of her own energy; she will show them how, she can teach them and persuade them, she is so able that they’ll catch it from her. (This is still faith in their rationality, in the omnipotence of reason. The mistake? Reason is not automatic. Those who deny it cannot be conquered by it. Do not count on them. Leave them alone.)

On these two points, Dagny is committing an important (but excusable and understandable) error in thinking, the kind of error individualists and creators often make. It is an error proceeding from the best in their nature and from a proper principle, but this principle is misapplied. . . .

The error is this: it is proper for a creator to be optimistic, in the deepest, most basic sense, since the creator believes in a benevolent universe and functions on that premise. But it is an error to extend that optimism to other specific men. First, it’s not necessary, the creator’s life and the nature of the universe do not require it, his life does not depend on others. Second, man is a being with free will; therefore, each man is potentially good or evil, and it’s up to him and only to him (through his reasoning mind) to decide which he wants to be. The decision will affect only him; it is not (and cannot and should not be) the primary concern of any other human being.

Therefore, while a creator does and must worship Man (which means his own highest potentiality; which is his natural self-reverence), he must not make the mistake of thinking that this means the necessity to worship Mankind (as a collective). These are two entirely different conceptions, with entirely—(immensely and diametrically opposed)—different consequences.

Man, at his highest potentiality, is realized and fulfilled within each creator himself. . . .Whether the creator is alone, or finds only a handful of others like him, or is among the majority of mankind, is of no importance or consequence whatever; numbers have nothing to do with it. He alone or he and a few others like him are mankind, in the proper sense of being the proof of what man actually is, man at his best, the essential man, man at his highest possibility. (The rational being, who acts according to his nature.)

It should not matter to a creator whether anyone or a million or all the men around him fall short of the ideal of Man; let him live up to that ideal himself; this is all the “optimism” about Man that he needs. But this is a hard and subtle thing to realize—and it would be natural for Dagny always to make the mistake of believing others are better than they really are (or will become better, or she will teach them to become better or, actually, she so desperately wants them to be better)—and to be tied to the world by that hope.

It is proper for a creator to have an unlimited confidence in himself and his ability, to feel certain that he can get anything he wishes out of life, that he can accomplish anything he decides to accomplish, and that it’s up to him to do it. (He feels it because he is a man of reason . . .) [But] here is what he must keep clearly in mind: it is true that a creator can accomplish anything he wishes—if he functions according to the nature of man, the universe and his own proper morality, that is, if he does not place his wish primarily within others and does not attempt or desire anything that is of a collective nature, anything that concerns others primarily or requires primarily the exercise of the will of others. (This would be an immoral desire or attempt, contrary to his nature as a creator.) If he attempts that, he is out of a creator’s province and in that of the collectivist and the second-hander.

Therefore, he must never feel confident that he can do anything whatever to, by or through others. (He can’t—and he shouldn’t even wish to try it—and the mere attempt is improper.) He must not think that he can . . . somehow transfer his energy and his intelligence to them and make them fit for his purposes in that way. He must face other men as they are, recognizing them as essentially independent entities, by nature, and beyond his primary influence; [he must] deal with them only on his own, independent terms, deal with such as he judges can fit his purpose or live up to his standards (by themselves and of their own will, independently of him) and expect nothing from the others. . . .

Now, in Dagny’s case, her desperate desire is to run Taggart Transcontinental. She sees that there are no men suited to her purpose around her, no men of ability, independence and competence. She thinks she can run it with others, with the incompetent and the parasites, either by training them or merely by treating them as robots who will take her orders and function without personal initiative or responsibility; with herself, in effect, being the spark of initiative, the bearer of responsibility for a whole collective. This can’t be done. This is her crucial error.

This is where she fails.