The message of the movie centers on the effects of growing up

I think the movie’s message centers on the effects of growing up:

The key to understanding this film, in my opinion, is to compare the lead characters in the beginning and the end. The fundamental occurrence is that Duane and Sonny grow up. At the beginning, they are high schoolers without a care in the world, as they play catch, laugh, make jokes, watch movies, and do whimsical trips to Mexico. But at the end, they are now adult men who have lost their virginity, suffered heartbreaks, confronted loss / deaths (ie Sam the Lion, the closing of the theater), and otherwise performed adult actions (eg enlisting in the army, working as a roughneck).

Although they grow up though, the big question that this movie asks is, “Have they improved? Are they better as adults, at the end, than as teenagers, at the start? What do they gain or lose?”

You might be inclined to say that they are better off in the opening, as they seem happy when they play catch and hang out with one another. But consider the moral improvements — they pull a prank on Billy, the retard, in an early scene. At the end though, Sonny pointedly gets angry at the men who don’t care that Billy just got hit with a car. The significance is that Sonny grew morally. Duane also had a job in Odessa, earning decent money (eg he has a nice car); and he bravely serves his country by enlisting to fight in Korea.

Thus, the movie shows that they may have been happier and more carefree in the opening, but by the end, they, as adults, have become better persons. A reasonable argument is that, however sad they seem, they are better persons at the end. Ultimately, the movie depicts the upsides and downsides to growing up