In the book "The Gift" by Cecelia Ahern, the theme revolves around the concept of living fully in the moment rather than being weighed down by past events or future anxieties. Ahern illustrates that those who are preoccupied with their past or constantly fearful of what lies ahead often miss out on the beauty of the present. The narrative encourages readers to reflect on their own lives and how habits and mindsets can affect their experiences.

Ahern uses the metaphor of people who "constantly looked over their shoulders" to signify the tendency of individuals to be preoccupied with their regrets or worries. This behavior can lead to missed opportunities and unexpected obstacles, as it distracts them from enjoying the journey of life itself. Overall, the book emphasizes the importance of embracing the present and finding joy in everyday experiences, urging individuals to let go of unnecessary burdens.