A man had better starve at once than lose his innocence in the process of getting his bread. If within the sophisticated man there is not an unsophisticated one, then he is but one of the Devil's angels. As ​we grow old, we live more coarsely, we relax a little in our disciplines, and, to some extent, cease to obey our finest instincts.
 Henry David Thoreau, Life Without Principle (1863). copy citation

Context

“The highest advice I have heard on these subjects was grovelling. The burden of it was,—It is not worth your while to undertake to reform the world in this particular. Do not ask how your bread is buttered; it will make you sick, if you do,—and the like. A man had better starve at once than lose his innocence in the process of getting his bread. If within the sophisticated man there is not an unsophisticated one, then he is but one of the Devil's angels. As ​we grow old, we live more coarsely, we relax a little in our disciplines, and, to some extent, cease to obey our finest instincts. But we should be fastidious to the extreme of sanity, disregarding the gibes of those who are more unfortunate than ourselves. In our science and philosophy, even, there is commonly no true and absolute account of things.” source