An extraordinary book. It has received, in my view, far too little attention. Scarcity of goods, services, resources and time have all been analyzed to death. The scarcity that exists between our ears — our cognitive bandwidth — has scarcely been analyzed at all. Mullainathan and Shafir show that this neurological constraint is fundamental in explaining all manner of behaviors and outcomes, from unaffordable borrowing to measured IQs. The public policy implications are potentially profound.