It would be useful to consider this excellent question by focusing on the character of Okonkwo. It is important to note that his character is built around a crucial paradox. He is famed for his manly strength and attributes in a culture that despises any form of weakness in men. Thus he strives and pushes himself to become as manly as possible, and despises any show of sentimentality of emotion. This leads him, for example, to participate in the death of his adopted son, Ikemefuna, even when he was advised not to. He joined in the murder, fearing that others would consider him weak if he stood back. This desire to constantly prove himself emerges from the life of his father, who was renowned for his laziness and lack of manly qualities. Note how, in Chapter Three, which gives us crucial background information about Okonkwo and his father, it talks about how this desperate desire to prove himself emerges:
But in spite of these disadvantages, he had begun even in his father's lifetime to lay the foundations of a prosperous future. It was slow and painful. But he threw himself into it like one possessed. And indeed he was possessed by the fear of his father's contemptible life and shameful death.
Thus it is ironic that the show of great strength and masculinity that Okonkwo exudes actually has its basis in a profound fear: that he will be identified with the same lack of strength and masculine qualities as his father. This is what drives Okonkwo to always work and to expect obedience and the same standards that he holds from his son, Nwoye. In his tremendous masculinity also lies the seeds of his own destruction, as he is unable to back down or negotiate.