Why Waiyaki did not fulfill his mission in The River Between?

Waiyaki attempts to find a middle ground for the Kikuyu (now Gikuyu) people by drawing on both traditional and European values and customs. His father’s belief in progress has motivated him to embrace the new and modern, but he cannot see that doing so has eroded the cohesion that enabled his people to resist the negative impacts of colonialism. Because they have lost their autonomy, just continuing to practice random customs will not bring it back.
As Waiyaki feels increasingly uncomfortable imposing the British values, he tries to turn the clock back by adhering to the old ways. His failure is accelerated by the actions of envious individuals, such as Kabonyi, who continues a grudge against Chege, Waiyaki’s father. In some respects a victim of his times, and in a period when there was really no viable middle ground, Waiyaki is also held back by his personality; as a natural compromiser, he cannot become the bold leader his people need.

In Ngugi wa Thiong'o's The River Between, Waiyaki is a young man whose mission in life becomes giving an education to his people, a village of the Kikuyu tribe of Kenya, while keeping their traditions safe from the destructive hands of white settlers.
There is conflict between villages of Kikuyu people who hold on to the traditional values of their heritage and those who have been converted to Christianity by missionaries, including the Kikuyu preacher Joshua. While Waiyaki becomes the leader of the "traditionalist" group of the Kikuyu, he sometimes finds himself torn between the values of the two cultures at war here, partially because of his love for Joshua's daughter, Nyambura.
Waiyaki ultimately realizes that education alone will not be enough to stop the conflict between the two groups, nor the reach of white colonialism. He decides to move forward with political action to unite the opposing groups of Kikuyu. However, at that point it is too late. Kabonyi has successfully planted doubts about Waiyaki's loyalty to his people, and the fates of both Waiyaki and Nyambura are to be decided by the Kiama.