Every choice is the tip of an unbroken causal chain

Sapolsky's foundational move is to insist that a decision made "in the moment" cannot be separated from the millions of prior causes that produced the brain making it. The neuron that fires to trigger an action fired because of its immediate inputs, which were shaped by the brain's structure that morning, which was shaped by that day's hormones and sleep, which trace back to childhood development, which traces back to genes and prenatal environment, which trace back to the choices and circumstances of one's parents and their ancestors.

He pushes readers to try isolating any single decision from this chain and notice that it can't be done — there is no point at which a self, uncaused by anything prior, simply steps in and decides. Even the sense of deliberating and weighing options is itself a biological process happening for biological reasons, not evidence of a free agent above the process.

Takeaway: the search for a gap in causation where "you" freely intervene turns up empty at every scale, from neurons to decades.