Why does Kino keep saying, "I am a man." This can be found at the end of Chapter 4 of The Pearl.The Pearl by John Steinbeck

After returning home from the pearl buyers' office, Kino
and his brother Juan Thomas discuss what has happened.  Juan Thomas warns Kino that if
he goes to the capital, Kino may meet with only more disappointment.  After his brother
leaves, Kino hears noises outside; upon looking outside, Kino steps out and is struck on
the the head. Cleaning his wound, Juana tells Kino,

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Kino, this pearl if evil.  Let us destroy it
before it destroys us.  Let us rush it between two stones.  Let us--let us throw it back
in the sea where it
belongs.

But, Kino looks
fiercely at her; against her protests, he declares himself man enought to fend off those
who would take it.  In order to silence Juana, Kino simply says, "I am a man."  When
Juana continues her protests, Kino merely answers, "Hush, ... I am a man. 
"Hush." 

Kino is a man like any other man.  He will defend
what is their property although he has broken "walls." and stepped out of "known
and trusted patterns.