Some of the reasons ("supporting arguments") that Gatsby cannot sustain his dream of recapturing the past and Daisy's love are the following:
- It is difficult to sustain the fiction of his background; he is not really of the socio-economic class of those with whom he wishes to associate and, therefore, he is never accepted. Gatsby himself gets confused in his fabrications; for example, he speaks of a battle in Italy that did not historically have the outcome he mentions. (Refer also to the scene in which the Sloanes reject him, and Tom Buchanan's continual questioning and investigation of Gatsby.)
- His source of wealth is illegal and its mystery is investigated and revealed. (There are rumors at the party...association with Meyer Wolfschiem...Tom's investigation.)
- Gatsby cannot really recapture the past because his memory of it with Daisy is unrealistic in the first place, and she is not in the present what he believes her to be (a "grail"). When they were younger, Daisy was only in love with being in love, not really in love with James Gatz. That she was "bought" by Tom Buchanan's $350,000 pearl necklace supports her materialistic, rather than loving, nature.
- After Jay goes to war her letters soon stop coming to him and she resumes her socialite life. In the present, when Gatsby, with his chivalry, tries to protect Daisy from being apprehended for the murder of Myrtle Wilson and stands guard under her window, she and her husband--"careless people" that they are--conspire in the kitchen on how to implicate Gatsby and he is betrayed by them later.
Even the title suggests that this main character has magically produced something and exists outside of reality. (The "great so-and-so" was a popular introduction to Vaudeville and circus acts, and such.) With this same motif of magic and myth, in Chapter Seven, Fitzgerald reveals that Gatsby's ethereal dream is tainted: "...his career as Trimalchio was over." Once he begins his affair with Daisy, Gatsby closes his home to others so that gossip will not start about Daisy. But, because she is married, their relationship is doomed by Tom's investigations and the power he has over Daisy. After all, there is only so much that a magician can do.
In his effort to retrieve the past and recapture the magic of his love for Daisy, James Gatz re-creates himself as Jay Gatsby in order to reflect his new persona, which has a certain mystique to it. Gatsby comes alive as the romantic hero of the materialistic American Dream, "delivered suddenly from the womb of his purposeless splendor." But, because his is a fictitious persona, Gatsby's life takes a tragic turn when it collides with reality.
I see two areas where Gatsby is very reluctant to accept reality. One leads to a direct consequence, and the other may have eventually caught up to Gatsby.
The first is that Gatsby is building his fortune through illegal methods. While it's never exactly stated what Gatsby does to become so horribly wealthy, it's more than likely he is at a minimum a bootlegger. The book takes place during prohibition and tons of real people (Capone) gained great wealth smuggling alcohol during this time. There's hints that Gatsby has some mob ties too, but bootlegging bears more evidence. The reality is that Gatsby is becoming wealthy by breaking the law and calling massive amounts of attention on himself through his parties. That's got to call the attention of law enforcement and eventually some kind of legal trouble.
The second area that Gatsby flat out ignores the reality of the situation is with Daisy. She's married. To a fairly aggressive guy. Did I mention that she is married? He has to know that eventually someone, like Tom, is going to find out. Gatsby is so deluded with himself, his wealth, and his infatuation with Daisy that he thinks he is untouchable. The "funny" thing, though, is that the consequence of his relationship is not delivered by Tom. Gatsby is killed by George Wilson, who thinks that Gatsby killed Myrtle, even though it was Daisy who killed Myrtle.