Fear is often seen as pathological, to be eliminated by expensive emotion-damping pharmaceuticals that have drastic side effects. Such therapies have indiscernible long-term success since they ignore why we have brains. This paper offers a new fundamental theory based on recognising that mental illness is bad decisionmaking—bad risk processing of external stimuli. Whiffs of danger—small risks (tiny chances and challenges)—generate little fears and hopes of whether an act will have a nice or nasty surprise. From enough whiffs of danger with rapid reliable feedback on whether the surprise is nice or nasty, and in adequate variety (sensual, physical, mental, psychological, social, ethical, spiritual) children learn the difference between luck and sensible choice, and adults maintain adequate decisionmaking—the author’s ‘whiffs of danger’ theory. Lack of whiffs constitutes risk starvation and can arise from under-challenge (the risks are too small) or over-challenge (the risks are too big). Boys’ ADHD springs from under-challenge in physical risks—the digital seduction—and over-challenge in mental, psychological, social risks—by faster maturing schoolgirls as teachers quit traditional boy favouritism. Boys’ IQ/maturity over-challenge could be cut by: (1) appropriate pre-school care; (2) single sex schools or in co-ed schools boys’ school entry postponed so one year older than their female classmates; and (3) boys praised for expressions of fears, hopes, not for emotion-damped macho utterances. Under-challenge underlies some panic attacks and epileptic fits, and a high proportion of depressions and dementias. Like schoolboys’ physical under-challenge, these under-challenges are reducible by compensating societal changes.