What is meant by the "unreality of reality, a promise that the rock of the world was founded securely on a fairy's wing"?
How are Gatsby's dreams initially a "satisafactory hint" of this?
This quote is in the beginning of chapter 6.
Jay Gatsby is a true romantic who believes that dreams and high ideals are essential elements that lead to success. His dreams signify the hope that he has to achieve his greatest aspiration: to once again be with his true love, Daisy Buchanan.
The metaphor is an apt description of the depth of Gatsby's dream. To him, the dream and reality are the same thing. The reference to a 'rock' indicates stability and strength - a solid foundation on which something can be built. To Jay, his dream is the foundation from which he can pursue and achieve his ideal. What makes the prospect more tantalizing is the fact that 'the rock of the world' is founded on a fantasy, 'a fairy's wing'. This is the nature of the true romantic - the dream becomes greater than reality and this provides the conviction that the dream is reality and not idle fancy - the lines are blurred. To a romantic such as Gatsby, there is no paradox.
In this sense then, Gatsby's dreams become a 'satisfactory hint' of this - that his dreams are real, that they have foundation and solidity, that they can be achieved. Gatsby has convinced himself that he will be able to win Daisy back and that she will want to be with him.
It is a pity then, that Gatsby has been so overwhelmed by his dream that he chooses to ignore the true reality: Daisy is married to an enormously wealthy man, she has a child, she is materialistic and manipulative, she has forsaken him, she is bored and seeks excitement and in some ways wants to get back at Tom; she is self-indulgent and spoiled and would never sacrifice her life of comfort and leisure to be with him.
Even when Daisy devastatingly tells him that he is 'asking too much', Jay persists and desperately clings to his dream. He drives her home and spends hours outside her mansion to ensure that she comes to no harm after she has accidentally killed Myrtle. It is this persistent hope that Nick admires so much but it is also this unrealistic and futile dream which, tragically, culminates in Gatsby's death.
Gatsby's dreams of impressing Daisy, winning her back and returning to the love they had are all unrealistic--Daisy is married, and, while Daisy and Gatsby may entertain an affair for a brief period of time, Daisy is married to Tom. Those bonds could not be broken easily by women in those days.
The quote from the narrator, Nick, is implying that things are always what we want them to be--what we may consider as a reality may be completely untrue. Gatsby has been so delusioned by the idea of winning Daisy back that he concentrates on nothing but that, when, in reality, she won't leave Tom. All the glamour and glitz of Daisy and Tom's life has overshadowed (originally) Nick's view of their marriage and what it's really like. We think something may be secure (a life, a relationship, an economy), but the rock we thought it was built on was just resting on a fairy's wing.