Answer:
If I could change only one characteristic of Gatsby's character, it would be inflexibility, because that is what prevents him from achieving his goals in the end.
Step-by-step explanation:
In F. Scott Fitzgerald's "The Great Gatsby", Jay Gatsby seems to have it all. He owns a mansion that looks like a castle, throws grand parties to hundreds of people every week, drives fancy and fast cars, etc. But what he wants the most is to have the love of his life by his side, Daisy. The problem is that Daisy is already married. They do have an affair, but Gatsby wants more. He wants Daisy to act as if her marriage, husband, and daughter never existed. He wants to ask her parents for their blessing and marry her, as he has dreamed and pictured over and over again.
However, there is a limit to what Daisy can and is willing to do. She cannot erase the past. She cannot pretend to have never been married. At a certain point in the story, they argue because she wants to run away with him, leave it all behind, but he does not. He wants to marry her. It is this inflexibility of his that costs them their dream. Had Gatsby accepted reality, taken Daisy's proposal to run away, and simply left with her, they could have been together, happily. But his insistence in doing things a certain way ends up ruining their affair and, tragically, even getting him killed.