“André Weil suggested that there is a logarithmic law at work: first-rate people attract other first-rate people, but second-rate people tend to hire third-raters, and third-rate people hire fifth-raters. If a dean or a president is genuinely interested in building and maintaining a high-quality university (and some of them are), then he must not grant complete self-determination to a second-rate department; he must, instead, use his administrative powers to intervene and set things right. That's one of the proper functions of deans and presidents, and pity the poor university in which a large proportion of both the faculty and the administration are second-raters; it is doomed to diverge to minus infinity.”

Day 18 (This saying was popularized by former U.S. Secretary of Defense Donald Rumsfeld in his "Rumsfeld's Rules" document, dating back to his tenure on the Ford Administration transition team.)
Reamde (2011), Part II: American Falls

As quoted in Business Etiquette for the Nineties : Your Ticket to Career Success (1992) by Lou Kennedy, p. 8
Variant: Always be a first rate version of yourself and not a second rate version of someone else.

as quoted by [N. Y. Mayall, Biographical memoir. Volume 41, Memoirs of the National Academy of sciences, National Academy of Sciences (U.S.), National Academy of Sciences, 1970, 179]
Attributed

Katherine Mansfield (1925)

Ibid.
Essays and reviews, From the Land of Shadows (1982)

War with Honour http://books.google.com/books?id=QmQDAAAAMAAJ&q="I+wrote+somewhere+once+that+the+third+rate+mind+was+only+happy+when+it+was+thinking+with+the+majority+the+second+rate+mind+was+only+happy+when+it+was+with+the+minority+and+a+first+rate+mind+was+only+happy+when+it+was+thinking", Macmillan War Pamphlets, Issue 2 (1940).

Liza Minelli, interviewed by Gene Shalit in the September 1977 issue of The Ladies Home Journal, as quoted in "Women in the News," https://news.google.com/newspapers?id=yXMjAAAAIBAJ&sjid=a2cEAAAAIBAJ&pg=5851%2C3647577 in The Sarasota Herald-Tribune (August 24, 1977), p. 6-D
Variant: But I'd rather be a first-rate version of myself than a second-rate version of somebody else.
Context: I don't sing them because I couldn't sing them as well as she did. I'd rather be a first-rate version of myself than a second-rate version of anybody.

Liza Minelli, as quoted in I Remember It Well (1975) by Vincente Minelli with Hector Arce, p. 395 https://books.google.com/books?id=D6jDtmiJCpkC&q=minelli+%22second-rate%22+%22first-rate+version%22&dq=minelli+%22second-rate%22+%22first-rate+version%22&hl=en&sa=X&ved=0CCoQ6AEwBGoVChMI0on3sqjdxgIVxHg-Ch1NhwVD; reprinted in "Judy and Liza, Part 3" https://news.google.com/newspapers?id=CfpjAAAAIBAJ&sjid=WuYDAAAAIBAJ&pg=7188%2C5401411 by Vincente Minelli, in The Sydney Herald (August 15, 1975), p. 8
Context: I couldn't sing Mama's special songs. I couldn't do them as well. I would rather present a first-rate version of myself than a second-rate version of Mama.

Liza Minelli, as quoted in "Liza Minelli 'Never Felt Better' Despite Tabloids' Whispers" https://news.google.com/newspapers?id=rmRGAAAAIBAJ&sjid=6ugMAAAAIBAJ&pg=3577%2C2269544 by Douglas J. Rowe, in TV Plus: The Schenectady Sunday Gazette Supplement (June 9, 1996), p. 4
Context: It really scared me to do what Mom did because I never did anything that she did. I promised her that I would never sing her songs, and I kept my promise. "You sing them better than anybody. I don't want to be a second-rate example of you. I want to be a first-rate example of myself."