The science writer Winifred Gallagher stumbled onto a connection between attention and happiness after an unexpected and terrifying event, a cancer diagnosis – "not just cancer," she clarifies, "but a particularly nasty, fairly advanced kind." As Gallagher recalls in her 2009 book Rapt, as she walked away from the hospital after the diagnosis she formed a sudden and strong intuition: "This disease wanted to monopolize my attention, but as much as possible, I would focus on my life instead." The cancer treatment that followed was exhausting and terrible, but Gallagher couldn't help noticing, in that corner of her brain honed by a career in nonfiction writing, that her commitment to focus on what was good in her life – "movies, walks, and a 6:30 martini" – worked surprisingly well. Her life during this period should have been mired in fear and pity, but it was instead, she noted, often quite pleasant.

Her curiosity piqued, Gallagher set out to better understand the role that attention – that is, what we choose to focus on and what we choose to ignore – plays in defining the quality of our life. After five years of science reporting, she came away convinced that she was witness to a "grand unified theory" of the mind:

“Like fingers pointing to the moon, other diverse disciplines from anthropology to education, behavioral economics to family counseling, similarly suggest that the skillful management of attention is the sine qua non of the good life and the key to improving virtually every aspect of your experience.”

This concept upends the way most people think about their subjective experience of life. We tend to place a lot of emphasis on our circumstances, assuming that what happens to us (or fails to happen) determines how we feel. From this perspective, the small-scale details of how you spend your day aren't that important, because what matters are the large-scale outcomes, such as whether or not you get a promotion or move to that nicer apartment. According to Gallagher, decades of research contradict this understanding. Our brains instead construct our worldview based on what we pay attention to. If you focus on a cancer diagnosis, you and your life become unhappy and dark, but if you focus instead on an evening martini, you and your life become more pleasant – even though the circumstances in both scenarios are the same. As Gallagher summarizes: "Who you are, what you think, feel, and do, what you love – is the sum of what you focus on."