Neither let mistakes and wrong directions — of which every man, in his studies and elsewhere, falls into many — discourage you. There is precious instruction to be got by finding that we are wrong. Let a man try faithfully, manfully, to be right, he will grow daily more and more right.

Thomas Carlyle (1795–1881) Scottish essayist and historian

Letter (1843-03-13), “Letter to a Young Man”
    (Source)

The letter was in response to an unidentified correspondent seeking advice on books to help him improve himself. It was eventually published / anthologized as an essay.