From Looking for History: Dispatches from Latin America, by Alma Guillermoprieto (Vintage, 2001), pp. 81-82:
Che was unable to deal with his disapproval of the course that Fidel was taking and his simultaneous love for the man; with his disillusionment with the Soviet Union and the self-satisfaction of the burgeoning Cuban bureaucracy; with the palace intrigues of the new regime (particularly those of Fidel’s brother Raúl); and, probably, with the gnawing awareness of his own failings as a peacetime revolutionary. It seems reasonable to interpret his decision to leave Cuba as Castañeda does—as the result of his need to get away from so much internal conflict. (In the course of explaining this decision, Castañeda provides an extraordinary account of the ins and outs of Cuban state policy, Cuban-Soviet relations, and Castro’s dealings with the United States.) Che was leaving behind a second wife, six children, his comrades, his years of happiness, and the revolution he had helped give birth to; none of these were enough to convince him that he belonged.
Guevara’s original intention was to return to his homeland and start a guerrilla movement there. A 1965 expedition to the Congo, where various armed factions were still wrestling for power long after the overthrow and murder of Patrice Lumumba, and his last stand in Bolivia, Castañeda writes, followed improbably from Fidel’s anxious efforts to keep Che away from Argentina, where he was sure to be detected and murdered by Latin America’s most efficient security forces. Castro seems to have felt that the Congo would be a safer place, and the question of whether it was a more intelligent choice doesn’t seem to have been addressed either by him or by the man he was trying to protect. (In Cairo, Jon Lee Anderson notes, Gamal Abdel Nasser warned Che not to get militarily involved in Africa, because there he would be “like Tarzan, a white man among blacks, leading and protecting them.”)
As things turned out, the Congo episode was a farce, so absurd that Cuban authorities kept secret Che’s rueful draft for a book on it—until recently, that is, when one of his new biographers, Taibo, was able to study the original manuscript. Guevara was abandoned from the beginning by Congolese military leaders, such as Laurent Kabila, who had initially welcomed his offer of help. He was plagued by dysentery and was subject to fits of uncontrollable anger, and emerged from seven months in the jungle forty pounds lighter, sick, and severely depressed. If he had ever considered a decision to cut bait and return to Cuba, that option was canceled weeks before the Congo expedition’s rout: on October 5, 1965, Fidel Castro, pressed on all sides to explain Che’s disappearance from Cuba and unable to recognize that the African adventure was about to collapse, decided to make public Che’s farewell letter to him: “I will say once again that the only way that Cuba can be held responsible for my actions is in its example. If my time should come under other skies, my last thought will be for this people, and especially for you.”
Guevara was sitting in a miserable campsite on the shores of Lake Tanganyika, bored, frustrated, and in mourning for his mother, when he was told that Fidel had publicized the letter. The news hit him like an explosion. “Shit-eaters!” he said, pacing back and forth in the mud. “They are imbeciles, idiots.”
Guevara’s final trek began at this moment, because once his farewell to Fidel was made public, as Castañeda writes, “his bridges were effectively burned. Given his temperament, there was now no way he could return to Cuba, even temporarily. The idea of a public deception was unacceptable to him: once he had said he was leaving, he could not go back.” He could not bear to lose face.
A few months later, having taken full and bitter stock of his situation, he made the decision to set up a guerrilla base—intended as a training camp, really—in southern Bolivia, near the border with Argentina. From there, he convinced himself, he would ultimately be able to spark the revolutionary flame in Argentina and, from there, throughout the world.