Those who know they are profound strive for clarity. Those who would like to seem profound strive for obscurity. For the crowd believes that if it cannot see to the bottom of something it must be profound. It is timid and dislikes going into the water.

[Tief sein und tief scheinen. — Wer sich tief weiss, bemüht sich um Klarheit; wer der Menge tief scheinen möchte, bemüht sich um Dunkelheit. Denn die Menge hält Alles für tief, dessen Grund sie nicht sehen kann: sie ist so furchtsam und geht so ungern in’s Wasser.]

Friedrich Nietzsche (1844-1900) German philosopher and poet

The Gay Science [Die fröhliche Wissenschaft], Book 3, § 173 (1882) [tr. Kaufmann (1974)]
    (Source)

Also known as La Gaya Scienza, The Joyful Wisdom, or The Joyous Science. (Source (German)). Alternate translations:

To Be Profound and to Appear Profound. -- He who knows that he is profound strives for clearness; he who would like to appear profound to the multitude strives for obscurity. The multitude thinks everything profound of which it cannot see the bottom; it is so timid and goes so unwillingly into the water.
[tr. Common (1911)]

Being Deep and Seeming Deep. -- Those who know they are deep strive for clarity. Those who would like to seem deep to the crowd strive for obscurity. For the crowd takes everything whose ground it cannot see to be deep; it is so timid and so reluctant to go into the water.
[tr. Nauckhoff (2001)]

Being Profound and Being Thought Profound -- Whoever knows that he is profound strives for clarity; whoever would like the crowd to think he is profound strives for obscurity. The reason for this is that the crowd thinks something is profound whenever it cannot see to the bottom of it; it is afraid of the water and hates to get its feet wet.
[tr. Hill (2018)]

Being Deep and Appearing Deep -- Whoever knows he is deep, strives for clarity; whoever would like to appear deep to the crowd, strives for obscurity. For the crowd considers anything deep if only it cannot see to the bottom: the crowd is so timid and afraid of going into the water.
[Source]

Whoever knows himself to be deep strives for clarity; whoever wants to appear deep to the masses strives for obscurity. For the masses consider anything to be deep that they cannot see the bottom of.
[Source]