Rick Hanson opens by presenting neuroscience research demonstrating that the human brain has an evolved negativity bias — a tendency to register and retain negative experiences more readily than positive ones — reflecting its evolutionary priority on threat detection over positive experience registration.

Why understanding this negativity bias matters:

• This evolved bias, while historically useful for survival, means positive experiences require more deliberate effort to be genuinely absorbed and retained compared to negative ones
• Understanding this bias as a normal neurological pattern, rather than a personal failing, provides important context for the book's subsequent practical techniques addressing it
• Hanson's neuroscience-grounded approach provides scientific credibility for the book's subsequent practical guidance on deliberately counteracting this bias

This opening establishes the book's neuroscientific foundation, explaining why deliberately cultivating positive experience requires specific effort given the brain's evolved negativity bias.