 Guevara was reluctant to return to Cuba , because Castro had made public Guevara 's " farewell letter " — a letter intended to only be revealed in the case of his death — wherein he severed all ties in order to devote himself to revolution throughout the world . As a result , Guevara spent the next six months living clandestinely in Dar es Salaam and Prague . During this time , he compiled his memoirs of the Congo experience and wrote drafts of two more books , one on philosophy and the other on economics . As Guevara prepared for Bolivia , he secretly traveled back to Cuba to visit Castro , as well as to see his wife and to write a last letter to his five children to be read upon his death , which ended with him instructing them : 
