What is ironic about Myrtle saying "You can't live forever"?
In chapter two of The Great Gatsby, Tom, Myrtle, and Nick are the primary guests at a party Myrtle is hosting for her neighbors. The apartment in the city is where Tom and Myrtle conduct their illicit affair, and on this day everyone gets a little out of line--in fact, Tom actually hits Myrtle, hard, in the nose when she taunts him about his wife Daisy. In the course of this evening, Myrtle makes this statement:
You can't live forever.
The irony of this line is that, not so very long from this time, Myrtle will be dead. She makes the statement in a rather flippant way, no doubt; however, she clearly has an intent when she breaks out of her house and runs into the path of the car she thinks Tom is driving--an act that costs her everything.
Myrtle’s statement is ironic but not just because she is killed later in the book. If anything, the book shows that she is speaking the literal truth. What irony there is in her statement stems from the context in which she makes this claim. Myrtle is telling Nick about how she first met Tom:
“It was on the two little seats facing each other that are always the last ones left on the train. I was going up to New York to see my sister and spend the night. He had on a dress suit and patent leather shoes, and I couldn’t keep my eyes off him, but every time he looked at me I had to pretend to be looking at the advertisement over his head. When we came into the station he was next to me, and his white shirt-front pressed against my arm, and so I told him I’d have to call a policeman, but he knew I lied. I was so excited that when I got into a taxi with him I didn’t hardly know I wasn’t getting into a subway train. All I kept thinking about, over and over, was ‘You can’t live forever; you can’t live forever.’”
Her expression is meant to convey how going with Tom was a desperate, once in a lifetime chance. In fact, it’s easy to see that Myrtle was pretty calculating in her approach to Tom; she “couldn’t keep her eyes off him” precisely because she hoped to attract his notice. Far from taking a desperate chance, Myrtle knew exactly what she was doing. She doesn’t mind at all being “kept” – she has no problem spending Tom’s money, and it is only when she tries to exert power over Tom’s emotional life – their fight over whether she should talk about Daisy – that she feels Tom’s real power over her (he breaks her nose). Myrtle’s statement about “not living forever” also suggests a “live for the day” mentality that belies the reality of her situation. That is, rather than forsaking duty to her husband for a life of immediate pleasure, she has exchanged one kind of misery for another.
It’s also worth pointing out the similarity between Myrtle’s “not living forever” and Gatsby’s desire to relive the past. One the one hand, Myrtle is all too willing to forget her past and throw in with Tom, while on the other hand Gatsby would sacrifice the wealth Myrtle craves for a return to his past with Daisy. In this case, the irony stems from the fact that either approach is doomed to failure; both Gatsby and Myrtle are grasping after something that leads, ultimately, to their deaths.