Never allow your mind to dwell on your own misconduct: that is ruin. The conscience has morbid sensibilities; it must be employed but not indulged, like the imagination or the stomach.

Robert Louis Stevenson (1850–1894) Scottish essayist, novelist, poet

Essay (1880-01/02?), “Reflections and Remarks on Human Life,” § 7.1 “Discipline of Conscience”
    (Source)

A collection of aphorisms and musings, first published in the Edinburgh Edition of his Works, vol. 28 (1898).