Never from Obstinacy take the Wrong Side because your Opponent has anticipated you in taking the Right One.
 
[Nunca por tema seguir el peor partido, porque el contrario se adelantó y escogió el mejor.]

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

The Art of Worldly Wisdom [Oráculo Manual y Arte de Prudencia], § 142 (1647) [tr. Jacobs (1892)]
    (Source)

(Source (Spanish)). Other translations:

Never to espouse a bad party in spight to an Adversary, who hath taken the better.
[Flesher ed. (1685)]

Never out of obstinancy take the wrong side, because your opponent has got before you and taken the right one.
[tr. Duff (1877)]

Never out of stubbornness hold to the wrong side, just because your adversary anticipated you, and chose the right.
[tr. Fischer (1937)]

Don’t defend the wrong side out of stubbornness, just because your opponent happened to arrive first and choose the right side.
[tr. Maurer (1992)]