What is crucial to realise about the character of Okonkwo is the way that he defines himself by everything that his father wasn't. His father was weak, effeminate and irresponsible in his laziness. Okonkwo therefore seeks to be different through his strength, his masculinity, and his industry. This is the defining goal of his life, and it is how he constructs his identity. Note what he says to Nwakibie when he goes to him and asks for some yam seeds to take and use them to have his own crop of yams:
I am not afraid of work. The lizard that jumped from the high iroko tree to the ground said he would praise himself if no one else did. I began to fend for myself at an age when most people still suck at their mothers’ breasts.
Okonkwo therefore defines himself through his strength and his industry. This has arisen from his own background and the way that his father's laziness meant that Okonkwo had to "fend for himself" from a very early age. This also explains why Okonkwo is constantly pressing himself to show his strong masculinity: he wrestles, he is a warrior, he is so scared of being called effeminate that he participates in Ikemefuna's death, even though he is like a son to him. Okonkwo seeks to turn himself into everything that his father was not, and as a result forces himself to engage in more and more acts that show his strong masculinity.