“The most valuable of all capital is that invested in human beings;”
Source: Principles of Economics, (1890), p. 468 (9th ed. 2009).
Context: If we compare one country of the civilized world with another, or one part of England with another, or one trade in England with another, we find that the degradation of the working-classes varies almost uniformly with the amount of rough work done by women. The most valuable of all capital is that invested in human beings; and of that capital the most precious part is the result of the care and influence of the mother, so long as she retains her tender and unselfish instincts, and has not been hardened by the strain and stress of unfeminine work.
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Alfred Marshall 5
British economist 1842–1924Related quotes

http://www.jstor.org/discover/10.2307/2495035?uid=3738776&uid=2&uid=4&sid=21104844992271
A more accurate translation, with respect to the context, might read: "Cadres are the key to everything"
In Russian: [...] из всех ценных капиталов, имеющихся в мире, самым ценным и самым решающим капиталом являются люди [...]. Кадры решают все!
Address to the Graduates from the Red Army Academies http://marx2mao.com/Stalin/GRA35.html. (4 May 1935); Variant translation: Human resources solve all!
Stalin's speeches, writings and authorised interviews

“Human resources are the most valuable assets the world has. They are all needed desperately.”
Source: Tomorrow Is Now (1963), p. 71

Source: The Limits To Capital (2006 VERSO Edition), Chapter 9, Money, Credit And Finance, p. 269

"The Organization of Labor," http://ebooks.library.cornell.edu/cgi/t/text/pageviewer-idx?c=nora;cc=nora;g=moagrp;xc=1;q1=The%20Organization%20of%20Labor;rgn=full%20text;cite1=Powderly;cite1restrict=author;view=image;seq=0122;idno=nora0135-2;node=nora0135-2%3A2 North American Review, vol. 135, no. 2, whole no. 309 (Aug. 1882), pp. 118–9.

Source: Myatt, David. Myngath - Some Recollections of the Wyrdful Life of David Myatt, CreateSpace, 2013, ISBN 978-1484110744

“Politeness and civility are the best capital ever invested in business.”
Ch. 17: "Be polite and kind to your customers" http://www.fourmilab.ch/etexts/www/barnum/moneygetting/moneygetting_chap18.html
Art of Money Getting (1880)