Everyone has a goal which appears to be great, at least to himself, and is great when deepest conviction, the innermost voice of the heart, pronounces it great.... This voice, however, is easily drowned out, and what we thought to be inspiration may have been created by the fleeting moment and again perhaps destroyed by it.... We must seriously ask ourselves, therefore, whether we are really inspired about a vocation, whether an inner voice approves of it, or whether the inspiration was a deception, whether that which we took as the Deity's calling to us was self-deceit. But how else could we recognize this except by searching for the source of our inspiration?

Writings of the Young Marx on Philosophy and Society, L. Easton, trans. (1967), p. 36 - Reflections of a Youth on Choosing an Occupation (1835)