One doesn't discover new lands without consenting to lose sight of the shore for a very long time.
Source: Les Faux-Monnayeurs (The Counterfeiters), André Gide, 1925
Genuine Gide, from The Counterfeiters (1925): 'On ne découvre pas de terre nouvelle sans consentir à perdre de vue, d'abord et pour longtemps, tout rivage.' The English here is a faithful translation. This is the authentic original of which q_0314 is the popular corruption.
Look for your own. Do not do what someone else could do as well as you. Do not say, do not write what someone else could say, could write as well as you. Care for nothing in yourself but what you feel exists nowhere else, and out of your self create, impatiently or patiently... the most irreplaceable of things.
Source: Les Nourritures terrestres (The Fruits of the Earth), André Gide, 1897
From the closing envoi of The Fruits of the Earth, addressed to Nathanaël. Standard translations end 'the most irreplaceable of beings' rather than 'of things', and the passage as given has been trimmed of its direct address to Nathanaël — worth normalizing against a published translation. The attribution itself is secure.