Self-assertion, n.
The act of asserting one's self, or one's own rights or claims; the quality of being self-asserting.
Shades of meaning
Fernald has no entry of its own for self-assertion; he lists it under assurance, egotism.
Where he writes about it:
Self-assertion is the claim by word, act, or manner of what one believes to be his due; self-conceit is an overestimate of one's own powers or deserts. — from egotism
Self-assertion at times becomes a duty; but self-conceit is always a weakness. — from egotism
Affirm has less of egotism than assert (as seen in the word self-assertion), coming nearer to aver. — from state