Keep matters for a time in suspense. Admiration at their novelty heightens the value of your achievements, It is both useless and insipid to play with the cards on the table. If you do not declare yourself immediately, you arouse expectation, especially when the importance of your position makes you the object of general attention. Mix a little mystery with everything, and the very mystery arouses veneration. And when you explain, be not too explicit, just as you do not expose your inmost thoughts in ordinary intercourse. Cautious silence is the holy of holies of worldly wisdom. A resolution declared is never highly thought of; it only leaves room for criticism. And if it happens to fail, you are doubly unfortunate.
Besides you imitate the Divine way when you cause men to wonder and watch.

[Llevar sus cosas con suspensión. La admiración de la novedad es estimación de los aciertos. El jugar a juego descubierto ni es de utilidad ni de gusto. El no declararse luego suspende, y más donde la sublimidad del empleo da objeto a la universal expectación; amaga misterio en todo, y con su misma arcanidad provoca la veneración. Aun en el darse a entender se ha de huir la llaneza, así como ni en el trato se ha de permitir el interior a todos. Es el recatado silencio sagrado de la cordura. La resolución declarada nunca fue estimada; antes se permite a la censura, y si saliere azar, será dos veces infeliz.
Imítese, pues, el proceder divino para hacer estar a la mira y al desvelo.]

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

The Art of Worldly Wisdom [Oráculo Manual y Arte de Prudencia], § 3 (1647) [tr. Jacobs (1892)]
    (Source)

See also § 253.

(Source (Spanish)). Alternate translations:

Not to be too free, nor open. It is the Admiration of Novelty that makes events to be valued. There is neither pleasure nor profit in playing ones Game too openly. Not to declare immediately, is the way to hold minds in suspence, especially in matters of importance, which are the object of universal expectation. That makes every thing to be thought a mystery, and the secret of that raises veneration. In the manner of expression one ought to have a care not to be too plain: and to speak with open heart is not always convenient in conversation. Silence is the Sanctuary of Prudence. A resolution made manifest was never esteemed. He that declares himself, is obnoxious to Censure: and if he succeeds not, he is doubly miserable.
We ought then to imitate the method of God Almighty, who always holds men in suspence.
[Flesher ed. (1685)]

Leave people in uncertainty about your purposes. [...] Imitate the heavenly powers in keeping men full of speculation and unrest.
[tr. Duff (1877)]

Maintain an air of uncertainty about your business. Admiration for the new is what bestows value upon the accomplished. To play with cards exposed is neither useful, nor in good taste. Create anticipation by not declaring your purpose, and especially where the height of your office commands public attention. Display a bit of mystery about everything, and by it further the respect in which you are held: even when you show your hand escape the obvious, -- just as in the daily round you do not disclose your inner self to everyone. A prudent silence is the sacred vessel of wisdom. Purpose declared was never highly esteemed and commits itself to criticism in advance, -- and should it fail, the misfortune is doubled.
Imitate, therefore, the ways of God in order to keep those about you watchful, and alert.
[tr. Fischer (1937)]

Keep matters in suspense. Successes that are novel win admiration. Being too obviouis is neither useful nor tasteful. By not declaring yourself immediately you will keep people guessing, especially if your position is important enough to awaken expectations. Mystery by its very arcaneness causes veneration. Even when revealing yourself, avoid total frankness, and don't let everyone look inside you. Cautious silence is where prudence takes refuge. Once declared, resolutions are never esteemed, and they lie open to criticism. If they turn out badly, you will be twice unfortunate.
If you want people to watch and wait on you, imitate the divinity.
[tr. Maurer (1992)]