“If you don't know where you're going, you won't go anywhere.”

When Pausch spoke of "You obviously don't know where the bar should be, and you're only going to do a disservice by putting it anywhere." he was quoting the advice of Andries van Dam on challenging his students after they already completed excellent performances on their first two week assignment.
The Last Lecture (2007)
Context: What he said was: "You obviously don't know where the bar should be, and you're only going to do a disservice by putting it anywhere." And boy was that good advice. Because what he said was, you obviously don’t know where the bar should be, and you’re only going to do them a disservice by putting it anywhere.

Source: Travels with Charley: In Search of America

When questioned as to the future of jazz, as quoted in Jet magazine (31 March 1960), p. 30

When You Come to a Fork in the Road, Take It!: Inspiration and Wisdom from One of Baseball's Greatest Heroes, Hyperion, 2002, ISBN 0786867752, p. 53
What Time Is It? You Mean Now?: Advice for Life from the Zennest Master of Them All, Simon and Schuster, 2003, ISBN 0743244532, p. 39
Yogiisms
Variant: You've got to be careful if you don't know where you're going because you might not get there.
Variant: If you don't know where you're going, you'll wind up somewhere else.[citation needed]
Variant: You got to be careful if you do not know where you are going, because you might not get there.

Source: A Higher Standard (2015), p. 189

Interview http://www.pga.com/pgachampionship/2003/news_interviews_081603_woodsqa.html (14 August 2003)

Source: Summer and the City: A Carrie Diaries Novel TV Tie-in Edition