Recklessness springs naturally from overoptimism. Left to its own highly persuasive devices, exultant mood will nearly always trump rational thought. It is in the amalgam of fever and reason that genius lies. Passions are like fire and water, observed the journalist Sir Roger L'estrange more than three hundred years ago: they are good servants but poor masters. Passion kept on a loose bit serves its master far better than if it is left unbridled. Brakes are necessary; the exuberant mind must preserve the capacity to take a dispassionate measure of itself and the object of its zeal. When it does not, the consequences can be devastating.