What is the theme in The Sheltering Sky by Paul Bowles?

Fear and regret is a theme in the story. Both Kit and Port Moresby are by fear and regret, and these impulsions drive them to catastrophe. For Port, a fear that his marriage is dissolving sends him into flight to the least hospitable regions of the Sahara. For Kit, a fear of some unnamed doom combined with guilt over her one-time infidelity with Tunner sends her spiraling into madness.