Big Sur features a number of major transformations. The first brings to light the rift between the 25-year-old, "King of the Beat Generation," happy Jack Kerouac as featured in his earlier novel, On the Road, and the nearly-40-year-old, cynical, run-down, and alcoholic Jack Kerouac reflected in Big Sur. Jack is forced to deal with the rift between his image and his self, a process that drives him to self-imposed isolation time and time again. His attempt to reconcile image and self is also partly responsible for his breakdown at the end of the novel. The novel also explores the way America has changed from the days of On the Road (1940s) to the days of Big Sur (1960). These changes, in Kerouac's mind, are largely negative: the country is bigger, dirtier, harsher, and less friendly. Big Sur illustrates how seemingly static places or landscapes can transform in the mind as a result of changes in perspective. In this case, Big Sur, California can seem at times beautiful, frightening, or lonely, depending on the mental state of the writer describing it.
Jack's madness in Big Sur is driven by a mid-life crisis.