What motivates Okonkwo?
Likely Okonkwo's biggest motivation is that of trying not to be seen as his father was, a weakling or a failure. This drives him to work incredibly hard, to fight like a lion and acquire two titles and become the veritable big man on campus in Umuofia. It also contributes to what is likely his biggest flaw, his single-mindedness combined with a wicked temper.
He is unable to think outside the bounds of Igbo culture and this governs many of the decisions he makes. Even after being exiled, he cannot think of any other system as having anything to offer and can only see the white man and christianity as a threat to which the only response is blind and angry resistance rather than any thought to compromise, etc.