A hundred years ago, a Russian priest who had trained himself into a physiologist watched a cat that was interrupted in the middle of a private act. The animal did not stop and turn to the interruption, as every rule of the day insisted it should. It bore down harder. From that stubborn creature Alexei Ukhtomsky drew a law of the nervous system he called the dominant: a single governing focus that gathers the whole mind toward one aim and quietly goes blind to everything else.

It is the reason you can finish a symphony, raise a child, or learn a trade. It is also the reason you cannot stop refreshing a screen, cannot forgive an old injury, and cannot see the person standing directly in front of you. The machine that builds a life and the machine that ruins one are, it turns out, the same machine at different settings.

In The Dominant Principle, Anna Kriger follows this forgotten discovery out of the laboratory and into ordinary life, where devotion curdles into obsession, conviction hardens into prejudice, and love decays into the failure to notice. Along the way she presses a question the modern science of the mind would rather not answer out loud: when we speak of “attention,” are we measuring anything at all, or only declaring it after the fact, once we already know how the story turned out?

Clear, humane, and quietly funny, this is a book about the hidden physiology of caring too much about one thing— and about the rarest discipline a human being can learn, which is to care, on purpose, about another.