Sleep and dreaming do not serve a single biological function, but are multifunctional states. Their functions include memory consolidation and integration, emotion regulation, creativity and problem solving, and preparation for waking life. One promising description level is that of dreaming as a general reality simulator. TST and SST describe two important purposes of simulation, namely successful coping with threats and social interactions. The merit of TST and SST is not so much that they conclusively explain the function of dreaming—although they represent the two classical principles of evolution, natural and social selection, there are also several other sleep and dream functions. TST and SST might be the only candidates among the multiple functions of sleep and dreaming that explain a particularly striking feature of dream phenomenology: dreaming is a remarkably realistic simulation of waking life, with the exception of a complete failure to successfully reflect on the current state of consciousness. Veridical insight into the dream state is biologically possible, as the phenomenon of lucid dreaming demonstrates. The fact that state reflectiveness is nevertheless generally absent in dreaming—dream lucidity is a rare phenomenon (Schredl & Erlacher 2011), and even during lucid dreams, lucidity lapses are common (Barrett 1992)—, suggests that state obliviousness during dreaming has an important function. As demonstrated here, among the different candidates for explaining the function of dreaming, TST and SST are the only ones that are capable of elucidating this specific function: state obliviousness is necessary for the effective simulation of threats and social interactions.
Even though recent neurobiological research has begun to reveal the neural correlates of state reflectiveness and, by contrast, of state obliviousness (Voss et al. 2009, 2014; Dresler et al. 2012), the specific neural mechanisms preventing the dreaming brain from realizing its full repertoire of cognitive capabilities are still largely unclear. Further research into these mechanisms might enable exciting opportunities for sleep and dream research by revealing simple methods of dream-lucidity induction. However, if such ways to induce a simulated reality under full control of its user become available too easily and broadly, this might also lead to unforeseen problems, as at least two important functions of dreaming—simulation of threats and social interactions—probably cannot be processed without state obliviousness. This proposed necessity generates a testable hypothesis: individuals with very frequent lucid dreams can be expected to differ from the majority of infrequent lucid dreamers in their threat-avoidance and social skills.