Most people think of genetics as a lottery: a fixed, inescapable destiny. In reality, genetic differences are more like unique operating systems, with different strengths and vulnerabilities. When understood, we can provide the inputs that nourish the weak points of our specific operating system, and make the strengths usable.

Your genome has roughly 3 billion letters, and the overwhelming majority make no measurable difference between you and the next person. Even among the variants that do make a difference, the number that influence a trait and the number that change what you should do are drastically different. A variant that moves your risk half a percentage point is real, but leaves the right action identical to knowing nothing at all. Only a handful are large enough to flip a decision, or explain a distinctly different lived experience. In practice these are the most useful, which is why I’ve chosen to focus on them below.