@Pokari Late response here, but I wanted to say that I find the moral to be quite well-expressed.
I Am Alive is very similar to the children's story of The Little Red Hen, who plants wheat and gathers other ingredients to make bread, asking other animals for help and receiving none. When her hard work culminates in a loaf of bread and the other animals ask for a share, she tells them they get as much bread as they contributed work, which is to say, none.
In terms of the social events depicted, I Am Alive is something of a sequel to The Little Red Hen (TLRH). Roughly speaking, the TLRH's events map up to and end where the boy enters college. The animals and the pencil have spent this time sponging off the success of a more industrious individual. I Am Live then continues as TLRH might have, were it longer. When the boy switches to a pen, the pencil goes on expecting her (and I contradict the translation of "his" because her attitude is depicted by a spurned woman) acclaim to continue, which overshadows any realization of the reality that circumstances have changed around her; that college submissions must be in pen, and that this truth is independent of the boy's or her wants.
When the boy intends to go on using her in the less award-winning, but still useful, act of studying, the pencil makes herself useless to spite the boy. Maybe the boy had kept her due to sentiment, or because he didn't want to buy more pencils. But by refusing to even act as a pencil, she throws away yet another reason for her to stay around. Her spite proves utterly counterproductive.
In the trash, we see a more pessimistic side of the wider situation. The soda can was purpose-built to be drained and discarded, perhaps roughly analogous to seasonal workers or people who lost the genetic lottery. His presence in the story seems to be an acknowledgement that not everyone who ends up at rock bottom could have averted their problems with hard work and good attitude (whereas the hen story limits itself to faulting the animals for their laziness); some folks just aren't made to last in society, or terrible circumstances squash good people flat. The can even accepts his lot, seeing the trash as his place now that he holds no soda (which is an awful thing to consider, but brutally honest on his part and not an entirely unheard-of attitude.) The pencil scorns the trash's inferiority, believing she does not belong there.
In truth, perhaps she doesn't. But she certainly put herself there. Unlike the can, she was made to be ever-giving. But she had tied her belief in her worth to another individual's accomplishments, even though her involvement was merely as a necessary but replaceable component. So much so that when circumstances betrayed her, she made the boy a target for her spite. And in doing so, she reached down into her greatest quality, her ever-givingness, and destroyed it. She would never have been shaved into uselessness as a wooden pencil would be. She would never have run out of eraser or lead as long as the boy replenished her. But she willfully took on mechanical failure, precisely the one thing that could invalidate her gifts, and then wondered why she had ended up in the trash.
This story plays out the idea that tying your self-worth to things you have not done (narcissism, essentially) sets up the world as a potential betrayer, and that such a world will someday make you a spiteful fool.
Better, then, to truly understand your accomplishments. The world will go on being arbitrary and full of misfortune, but when it strikes you, at least your first reaction will not be to scorn everyone around you and then wonder why things have gotten worse for you.