What does everyone have that they can always count on?

Everyone has a circadian rhythm, which is a natural, internal process that regulates the sleep-wake cycle and repeats roughly every 24 hours. This rhythm is controlled by the body's internal clock, located in the brain, specifically the suprachiasmatic nucleus of the hypothalamus. It helps regulate various biological processes, such as hormone production, metabolism, and body temperature, ensuring that individuals can always count on a consistent pattern of physiological functions throughout the day.