Max Weber, in "Science as a Vocation":
Do you in all conscience believe that you can stand seeing mediocrity after mediocrity, year after year, climb beyond you, without becoming embittered and without coming to grief? Naturally, one always receives the answer: 'Of course, I live only for my "calling."' Yet, I have found that only a few men could endure this situation without coming to grief.
from "Science as a Vocation," found in English translation online at http://mail.www.anthropos-lab.net/wp/wp-content/uploads/2011/12/Weber-Science-as-a-Vocation.pdf, (accessed 20121027). Original citation: Published as "Wissenschaft als Beruf," Gesammlte Aufsätze zur Wissenschaftslehre (Tübingen, 1922), pp. 524-55; originally a speech at Munich University, 1918, published in 1919 by Duncker & Humblodt, München. From H.H. Gerth and C. Wright Mills (Translated and edited), From Max Weber: Essays in Sociology, pp. 129-156, New York: Oxford University Press, 1946.