What is the main characteristic of Delayed Sleep Phase disorder?

The main characteristic of Delayed Sleep Phase Disorder is the inability to fall asleep and awaken at desired times, which aligns with the symptoms of this specific circadian rhythm sleep disorder. Individuals with this condition typically have a significantly delayed sleep onset and wake times, often going to bed and waking up much later than the conventional schedule. This misalignment often leads to difficulties in maintaining the desired schedule for social, occupational, or academic activities.

Option B refers to sleep disorders related to incomplete awakenings, which are more associated with disorders such as sleepwalking or confusional arousals. Options C and D deal with parasomnias, including sleepwalking, sleep terrors, and REM sleep behavior disorder, which involve specific behaviors occurring during sleep rather than the timing difficulties central to Delayed Sleep Phase Disorder. Thus, the identified answer accurately reflects the essence of Delayed Sleep Phase Disorder's core issues.