The uncertainties of life put every person on Earth perpetually at risk. Some risks are self-inflicted, and humanity faces an ongoing risk of extinction. These concerns haunt Green, and he mentions them often in the book. He struggles to come to terms with these dangers as they affect him personally, and he exhorts people to wake up to the harm we inflict on the environment and solve this crisis before it’s too late.

One of the most jarring and troubling facts of human life that it’s finite. People have faced this since humans walked the Earth, and the reality of it still confronts us today despite our health breakthroughs and other scientific advances. A serious illness brought this home to Green: “I know now with a viscerality I didn’t before that consciousness is temporary and precarious” (4). The shortness of life can seem brutally unfair. We may feel that it renders pointless our efforts to make a difference, since we and those to whom we contribute will, all too soon, be gone—our work forgotten, its effects vanishing with time.

Green casts about for some meaning in the shortness of our lives, and he finds it in hope and love: hope that he and others can find happiness in the present, and love for others, which he believes transcends death and can bind us to each other eternally.