The greatest skill in cards is to know when to discard; the smallest of current trumps is worth more than the ace of trumps of the last game.

[La mejor treta del juego es saberse descartar: más importa la menor carta del triunfo que corre que la mayor del que pasó.]

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

The Art of Worldly Wisdom [Oráculo Manual y Arte de Prudencia], § 31 (1647) [tr. Jacobs (1892)]
    (Source)

(Source (Spanish)). Alternate translations:

The true skill at play, is to know how to discard. The lowest Card that turns up, is better than the highest of the former dealing.
[Flesher ed. (1685)]

The great trick in cards lies in knowing what to discard: and the deuce of a suit that is trump, is more valuable than the ace of a suit that was.
[tr. Fischer (1937)]

The trick is to know what cards to get rid of. The least card in the winning hand in front of you is more important than the best card in the losing hand you just laid down.
[tr. Maurer (1992)]