That to be interested in something, is not the same as self-assertion.
We can add to the word ”self-assertion” multifold meanings.
In art of life self-assertion is based on becoming something, and therefore anxiety.
But if a boy for instance is interested in becoming an engineer, because he is inclined towards raising beautiful buildings, to create wonderful bridges, to build excellent roads, then this is because he loves that act; and that is not self-assertion.
It is an expression of what he is, and therefore there is no anxiety.
In love there is no anxiety.