Things fall apart, nice...
Answer: Okonkwo and Obierka are best friends, but their personalities don't exactly match. Obierika is the kind of person who refrains from using violence, open for change, thinks before they act. On the other hand, Okonkwo doesnt think before he acts, he resorts to violence when things dont go his way, and he able to cope with new cultural changes.
Obierika ctitizized Okonkwo because Obierika was against the fact okonkwo took part in Ikemefunas death. Obierika stated his actions were something the Earth wouldn't please.