Determination in a single instance is an expression of courage; if it becomes characteristic, a mental habit. But here we are referring not to physical courage but to courage to accept responsibility, courage in the face of a moral danger. This has often been called courage d’esprit, because it is created by the intellect. That, however, does not make it an act of the intellect: it is an act of temperament. Intelligence alone is not courage; we often see that the most intelligent people are irresolute. Since in the rush of events a man is governed by feelings rather than by thought, the intellect needs to arouse the quality of courage, which then supports and sustains it in action.

Looked at in this way, the role of determination is to limit the agonies of doubt and the perils of hesitation when the motives for action are inadequate.

[Die Entschlossenheit ist ein Akt des Muthes in dem einzelnen Fall, und wenn sie zum Charakterzug wird, eine Gewohnheit der Seele. Aber hier ist nicht der Muth gegen körperliche Gefahr, sondern der gegen die Verantwortung, also gewissermassen gegen Seelengefahr gemeint. Man hat diesen oft courage d’esprit genannt, weil er aus dem Verstande entspringt, aber er ist darum kein Akt des Verstandes, sondern des Gemüths. Blosser Verstand ist noch kein Muth, denn wir sehen oft die gescheitesten Leute ohne Entschluss. Der Verstand muss also erst das Gefühl des Muthes erwecken, um von ihm gehalten und getragen zu werden, weil im Drange des Augenblicks Gefühle den Menschen stärker beherrschen als Gedanken.

Wir haben Uer der Entschlossenheit diejenige Stelle angewiesen, wo sie bei nicht hinrechenden Motiven die Qualen der Zweifel, die Gefahren des Zauderns heben soll.]

Karl von Clausewitz (1780-1831) Prussian soldier, historian, military theorist

On War [Vom Kriege], Book 1, ch. 3 “On Military Genius [Der Kriegerische Genius],” (1.3) (1832) [tr. Howard & Paret (1976)]
    (Source)

(Source (German)). Alternate translations:

Resolution is an act of courage in single instances, and if it becomes a characteristic trait, it is a habit of the mind. But here we do not mean courage in face of bodily danger, but in face of responsibility, therefore to a certain extent against moral danger. This has been often called courage d'esprit, on the ground that it springs from the understanding; nevertheless, it is no act of the understanding on that account it is an act of feeling. Mere intelligence is still not courage, for we often see the cleverest people devoid of resolution. The mind must, therefore, first awaken the feeling of courage, and then be guided and supported by it, because in momentary emergencies the man is swayed more by his feelings than his thoughts.

We have assigned to resolution the office of removing the torments of doubt, and the dangers of delay, when there are no sufficient motives for guidance
[tr. Graham (1873)]

Resolution is an act of courage in a single instance, and, if it becomes a characteristic trait, a habit of the mind. But here we do not mean courage in facing physical danger, butr courage in facing responsiblity, therefore to a certain extent in facing moral danger. This has often been called courage d'esprit, on the ground that it springs from the intellect, but it is not on that account for an act of the intellect but one of feeling. Mere intellect is not quite courage, for we often see the cleverest people devoid of resolution. The intellect must first, therefore, awaken the feeling of courage to be maintained and supported by it, because in emergencies of the moment man is governed more by his feelings than by his thoughts.

We have assigned to resolution the office of removing the torments of doubt and the dangers of hesitation when there are no sufficient motives for guidance.
[tr. Jolles (1943)]