Her vanity leaped to the aid of her desire to believe, making belief a certainty. If he knew she loved him, he would hasten to her side. (4.73)
Scarlett's vanity is considerable, and it often leaps to the aid of her belief. In fact, this quote about Ashley from early in the book mirrors her certainty at the end of the book that she can get Rhett back.
"Why all we have is cotton and slaves and arrogance. They'd lick us in a month." (6.116)
Here Rhett is explaining to the other Confederates that their plans for victory are ridiculous. As with Scarlett, arrogance and conceit play a big part in dreams and hopes for Southern victory. Pride cometh before the face plant.
She was less frightened also because life had taken on the quality of a dream, a dream too terrible to be real. It wasn't possible that she, Scarlett O'Hara, should be in such a predicament, with the danger of death about her every hour, every minute. (19.13)
Scarlett's vision and dream of herself as a Southern belle, and her belief that all will be well, persists even as Atlanta falls and everything slides toward chaos. Her dreams are something of a protection—which is the case throughout the novel. Part of why she's so tough is that her dreams are so tough; they protect her from realizing that there's no hope, and so she often wins even when things are hopeless. She is insulated from despair.
"I'm going to live through this, and when it's over, I'm never going to be hungry again. No, nor any of my folks. If I have to steal or kill—as God is my witness, I'm never going to be hungry again." (25.53)
This is perhaps the most famous line in the novel, and one of the most famous lines in American literature. It's also a dream that comes true; Scarlett does kill and steal, and she manages not to be hungry. There are downsides there, though, which she doesn't really consider.
"There are things more important now than plowing, Sugar. And scaring the darkies and teaching the Scallawags a lesson is one of them. As long as there are fine boys like Tony left, I guess we won't need to worry about the South too much." (37.57)
Frank is feeling hopeful for the South because there are boys like Tony Fontaine willing to murder black people. It's a painful reminder that the dreams of the white South, throughout the novel, are built on systematic violence and cruelty to black people.
Oh, some day! When there was security in her world again, then she would sit back and fold her hands and be a great lady as Ellen had been. She would be helpless and sheltered, as a lady should be, and then everyone would approve of her. (38.100)
Scarlett dreams of being like her mother—but she wouldn't actually really much like it. In this sense, she's somewhat like Gerald, who loves Ellen without being anything like her. Everyone would have been happier, maybe, if Scarlett could have just married Melanie (a great lady like Ellen) at the beginning of the novel.
"What would a child do with the moon if it got it? And what would you do with Ashley?...you are such a fool you don't know there can't ever be happiness except when like mates like." (54.64)
Rhett explains to Scarlett that she wouldn't like Ashley if she got him; her dreams are self-deceptions. He's right… but he could maybe have talked to himself instead, since he's constitutionally unhappy when he gets what he wants, too. He wants Scarlett to marry him, she does, and he's sad; he wants her to love him, and she does, and he's sad. If he's so smart, why's he so dumb?
"She is the only dream I ever had that lived and breathed and did not die in the face of reality." (61.119)
Ashley is here saying that Melanie was a dream that came true. Is this really a tribute to her, though? She wasn't a dream; she was his wife, a real person. Maybe he could have treated her better if he wasn't trying to make her a dream, huh?
"He never really existed at all, except in my imagination," she thought wearily. "I loved something I made up, something that's just as dead as Melly is, I made a suit of pretty clothes and fell in love with it." (61.140)
Scarlett finally realizes that the Ashley she made up isn't real. This is doubly true since, you know, Ashley is really just a character in a book. So the dream Ashley of Scarlett's imagination isn't really any more real than the "real" Ashley. What do you think that says about the novel's portrayal of the Civil War? Is that real, or are some things (like, say, the evils of slavery) left out?
She could get Rhett back. She knew she could. There had never been a man she couldn't get, once she set her mind upon him. (63.136)
Even with her marriage ruined, the love of her life revealed as worthless, and her best friend dead, Scarlett's still dreaming. Is she an idiot or a hero? Maybe both?