From the first chapter of the novel, the reader learns that Okonkwo loathes his father Unoka. The worst qualities that a man can have (in Okonkwo's mind) were weakness and laziness and he felt his father embodied these perfectly. And this drives him to be unwilling to ever consider too deeply his actions. As long as they are manly and strong and lead down the traditional path to success in Igbo culture, they are the right actions.
Because of this, he ignores rather wise warnings like that of Ogbuefi who warns him not to take part in Ikemefuna's killing. This causes Okonkwo great distress but he is unable to learn any lesson from it and he goes on to make similar errors again.
When he sees that the people of Umuofia have, in his mind, given in to the Christians and the white man he believes that the only way forward is to fight back. Rather than consider that there might be some value to what the white settlers bring, he attacks the problem the only way he knows how and ultimately fails. Again, his fear of being seen weak or womanly prevents him from ever considering things too deeply or listening to wise friends like Obierika who try to pull him back from the edge so often.