Without courage, wisdom bears no fruit.

[Sin valor es estéril la sabiduría.]

Baltasar Gracián y Morales (1601-1658) Spanish Jesuit priest, writer, philosopher

The Art of Worldly Wisdom [Oráculo Manual y Arte de Prudencia], § 4 (1647) [tr. Maurer (1992)]
    (Source)

(Source (Spanish)). Alternate translations:

Knowledge is barren, if Valour do'nt accompany it.
[Flesher ed. (1685)]

Knowledge without courage is sterile.
[tr. Jacobs (1892)]

Without courage, the mind is dead.
[tr. Fischer (1937)]