Why does Okonkwo kill the messenger? How does his action succeed or fail?

Okonwo kills the messenger as an act of defiance against the white oppressor. The indignities forced Okonkwo and his people by the British eventually prove to be too much for him. Okonkwo is not good with change and this new shift in culture is too much for Okonkwo to handle. After an act of defiance which goes unsupported by his people, Okonkwo gives in to despair. He kills himself, partly so that he will not be executed under the white man's laws and partly because he is grieving for the death of his people.