But he did it to me first.
But he got more than I did.
He's looking at me.
He's on my side of the room.
He's touching my toy.
It's mine because I had it first.
I was here first.
I did it because he needs to know how it feels.
At least I'm doing better than he did.
I'm not going to do my chores if he isn't going to do his.
He also did something wrong.
I want what I want.
Whatever I want is good for me.
It's true because I believe it.
It's true because it makes me happy.
Behind these are standard informal fallacies that distract from sound reasoning and confuse the category of truth with feelings:
Appeal to pity
The hope is that as a child grows up fallacious thinking is replaced with sound argumentation. What if this never happens and the adult becomes a leader? Or enters the Academy?
All of these cases involve a child-like understanding of what is just or fair. When they persist into adulthood they become a childish understanding of justice. Blame the other person for my own failings; compare what I have with what others get; justify my wrong doing or poor performance by pointing out another person's problem. Avoid personal responsibility and blame my environment and other people.
Hopefully the child learns that equality in amount of cookie and fairness are not always the same. That he should be happy to get any amount of cookie. That someone looking at you can't hurt you. To compare our performance with the best we can be rather than comparing to others. To take personal responsibility and not get involved in self-justification which is usually a result of self-deception about one's condition.
Almost all of these, perhaps all, involve a form of envy, anger/wrath, greed, gluttony, autonomy, unbelief, and other harmful attitudes that one hopes to outgrow.
One possible explanation of why these attitudes persist into adulthood is a continued belief that material pleasure is the good. Noticing that such pleasure is unevenly distributed in life makes the adult regress to the "amount of cookie complaint." Whereas the child is still learning to think about what is good, the adult has no excuse in failing to know what is good and no excuse for believing material pleasure is the good. Furthermore, unbelief leads this adult to have no satisfactory explanation for why the world is as it is besides unfair historical contingencies shaped by the greed of others.
Yet, in keeping with the theme of this blog, growing out of these deadly attitudes requires correctly identifying what is good in contrast to our many competing wants, and in so doing realizing that no one can take what is truly good from you nor can they keep you from the good.