Aggression and assertiveness are very different. Assertiveness comes from self-confidence and clear thinking, often from a desire to contribute. Aggression stems from insecurity and usually prompts violence or fear. Know the difference.
Here's one of my favorite poems, Invictus by William Ernest Henley. I feel it could be at the helm of an old ship navigating turbulent waters.
Out of the night that covers me,
Black as the pit from pole to pole,
I thank whatever gods may be
For my unconquerable soul.
In the fell clutch of circumstance
I have not winced nor cried aloud.
Under the bludgeonings of chance
My head is bloody, but unbowed.
Beyond this place of wrath and tears
Looms but the Horror of the shade,
And yet the menace of the years
Finds and shall find me unafraid.
It matters not how strait the gate,
How charged with punishments the scroll,
I am the master of my fate,
I am the captain of my soul.