The 'first-night effect' refers to the difficulty many people experience when trying to sleep in unfamiliar settings, such as hotels or new locations. This phenomenon occurs even when individuals feel physically tired, largely due to a mix of biological and psychological reasons. As the body readies itself for sleep by reducing core temperature and increasing melatonin production, it also relies heavily on familiar environmental cues to signal that it’s time to rest. When these cues are disrupted, sleep can become elusive.

In a new environment, various factors can compete with the body's natural cues for sleep. Loud noises, unwelcome temperatures, and changing light conditions can exacerbate anxiety and insomnia. For instance, the sounds of traffic or uncomfortable bedding can heighten alertness and prevent relaxation. Therefore, the brain struggles to transition into sleep mode, as it is biologically programmed to remain vigilant in unfamiliar surroundings, often to ensure safety and security.

This struggle to sleep in new environments has implications not only for travelers but also for those who may need to adjust to new living conditions, like students in dorms or anyone relocating. Understanding these challenges can help individuals develop strategies to mitigate the 'first-night effect', such as creating a sleep-conducive environment through relaxation techniques and familiar routines, which may aid in better sleep quality even when away from home.