"Uncontrollable events" refers to things that happen that we cannot control or influence. These events occur unexpectedly and we can't do anything to change or stop them. Full definition
Other times they feel an illusory sense of power over uncontrollable events. (scientificamerican.com)
Full of guilt, the Professor claimed to have activated a chain reaction of uncontrollable events that would destroy the humanity and would leave the Earth close to the end... To know the reasons of his death, Filby goes back to the Professor's laboratory and discovers a strange spherical machine, which seems partially dismantled. (gamebra.com)