Fear
To inspire terror in others, one must plumb one's own depths unto the ultimate horror. To truly understand the sudden panic that reshapes the sternest visage from sneer to scream, one must invite the nightmare inside oneself and allow it to have its way. Though hair may turn from black to white over the course of a single night, the lessons learned are well worth employing against one's enemies.
Overwhelm, give no quarter, allow no retreat, scare your foe into submitting, then kill him; these are the lessons Fear teaches so well. If one must fight, do not fight fairly, and if at all possible, arrange to have others face threats in your place. Listen well, child, for these are the lessons Fear teaches.
Other Aspects
Valor
The concept of Valor is the greatest of the Great Lies.
The valorous lie to themselves and to others, hiding the cowardice that nests in all breasts beneath a veneer of self-delusion. As the Roman historian Tacitus observed, "Valor is of no service, chance rules all, and the bravest often fall by the hands of cowards."
Thus the valorous reap but horror for their arrogance in appointing to themselves the qualities of bravery and foresight. Fear makes a mockery of all such conceits, dissolving them in doubt, dread, revulsion, and the final terror.
Madness
Driving Fear's spike into the valorous is rewarding because it is difficult -- agitating the mad is far easier, though results are sometimes questionable. Who can tell whether the mad scream in terror, or because imaginary voices impel them? Do the mad break and fail because horror has overcome them, or because they pursue some cunning strategy only a lunatic could devise?
When the battle concludes, the corpses of the mad reveal not whether they succumbed to their own psychoses or to heart-stopping, nauseating Fear.
Passion
In truth, Passion is a better shield against dismay than Valor. Where Valor seeks to hold itself above apprehension through adherence to a brittle principle, the passionate are filled from stem to stern with fury, battle-frenzy, berserker-rage. Against a mind already suffused with rampant emotion, Fear's tactics sometimes fail to insinuate. An abominable monstrosity sure to set the mad to babbling and lance the valorous with disquiet is just one more foe to the passionate.
But Fear knows no heart is immune to worry, and even the most passionate pause, and in that pause, phantasms pounce.