As we go catching and catching at this or that corner of knowledge, now getting a foresight of generous possibilities, now chilled with a glimpse of prudence, we may compare the headlong course of our years to a swift torrent in which a man is carried away; now he is dashed against a boulder, now he grapples for a moment to a trailing spray; at the end, he is hurled out and overwhelmed in a dark and bottomless ocean. We have no more than glimpses and touches; we are torn away from our theories; we are spun round and round and shown this or the other view of life, until only fools or knaves can hold to their opinions.

Robert Louis Stevenson (1850-1894) Scottish essayist, novelist, poet
Essay (1878-03), “Crabbed Age and Youth,” Cornhill Magazine, Vol. 37
    (Source)

Collected in Virginibus Puerisque and Other Papers, ch. 2 (1881).