“You can be anyone you want, but you must be real. ”

Original: Chi vuole esserti accanto deve saper aggiungere, non togliere.
Source: prevale.net

Source: City of Glass

Source: Oceans of Fire

In late January 2016, as quoted in "The Obama Doctrine" by Jeffrey Goldberg, in The Atlantic (April 2016) http://www.theatlantic.com/magazine/archive/2016/04/the-obama-doctrine/471525/
2016

Though Keillor has been quoted on the internet and in print as having made this or a similar remark, such expressions have been made by others, and may have originated with Billy Sunday, who is quoted as having said "Going to church on Sunday does not make you a Christian any more than going into a garage makes you an automobile!" in Press, Radio, Television, Periodicals, Public Relations, and Advertising, As Seen through Institutes and Special Occasions of the Henry W. Grady School of Journalism (1967) edited by John Eldridge Drewry.
Disputed
Variant: Going to church no more makes you a Christian than standing in a garage makes you a car.

Love – That’s All Cary Grant Ever Thinks About (1964)

Source: Dreamsnake (1978), Chapter 9 (p. 205)

Source: The Bed of Procrustes: Philosophical and Practical Aphorisms (2010), p. 39