A Vicious Cycle
So faulty simulations, evaluations, and beliefs about the future may drive depression, and these three problems interact with one another to create the hallmark characteristics of major depressive disorder: first and foremost, depressed mood, irritability, low energy, low motivation, apathy, and suicide. We do not think, however, that poor prospection causes all symptoms of depression in the Diagnostic and Statistical Manual (5th ed.; DSM-5; American Psychiatric
Association, 2013); for example, it is more difficult to see how prospection would cause concentration problems, loss of pleasure, or psychomotor agitation. This may be because the DSM-5 does not carve nature at the joints; major depressive disorder is not a single distinct thing (Gorman, 1996; Haslam, 2003; Haslam & Beck, 1994; Ruscio & Ruscio, 2000). Regardless, faulty prospection is neither necessary nor sufficient; rather we hypothesize that faulty prospection is the primary cause in that it accounts for more of the variance at the psychological level than other causes, such as the negative view of the self, negative view of the world, and PES.
We also propose that faulty prospection sets up a vicious cycle. It produces depression, and depression, in turn, potentiates poorer prospection in at least three ways. First, depressed people withdraw socially, limit their activities, and rely on avoidance, and thus have fewer positive experiences (Holahan, Moos, Holahan, Brennan, & Schutte, 2005; Kasch, Rottenberg, Arnow, & Gotlib, 2002). Because of this, they have impoverished raw material for constructing positive future scenarios. Second, depression leads people to act in ways that create stressful experiences and interpersonal conflicts (Hammen, 2006), and these negative experiences provide raw material for vivid negative simulations of the future. Third, simply being in a sad mood makes one more likely to remember a negative past and imagine a negative future (Miloyan et al., 2014; O'Connor & Williams, 2014).