As a person grows, his animal soul and evil inclination grow with him.
A child has a limited understanding of the world, and correspondingly his evil inclination is also limited.
A three-year-old wants construction paper.
Then, as an adult whose understanding of the world has broadened, he desires banknotes.
However, although the object of his desire has changed, the nature of his relationship to objects, of how his animal soul is controlled by and drawn after his drives, has not changed.
An adult does not possess the desires of a child.
He has not outgrown them, but they have changed their form.
In essence, he has the same desires-perhaps even in stronger form.
The commentators observe that the teaching "Jealousy, desire, and honor take a person out of the world" (Avot 4:21) refers to the three periods of a person's life.
A child's most outstanding emotion, the one that most strongly affects him and drives him to act, is jealousy.
A child does not so much desire an object as envy the person who possesses it.
Then, as a person grows to adulthood, his jealousy lessens and his desire begins to burn.
Afterward, as he ages, his desires lessen, to be replaced by the chase for honor.
Despite the differences among them, jealousy, desire, and honor all share the same relationship within a person: they are all expressions of the animal soul that controls him.
The Baal Shem Tov's last words were the verse "Do not bring me to the foot of pride" (Psalms 36:12; Shivchei haBesht).
Similarly, the last words of the Holy Ari were "Guard me from pride" (see Notzar Chesed 4:4).
These words are an expression, perhaps extreme, of the ongoing battle against the evil inclination – in these cases, to the very last moment.
Even a person who has overcome the evil inclination continues to be oppressed by the obstacle of his pride.
–Rabbi Adin Steinsaltz
From Understanding the Tanya by Rabbi Adin Steinsaltz