I gave the quote to "ask Jeeves" (www.ask.com
), and came back with all kinds of results!
"Mile by mile, life's a trial. Yard by yard, life is hard. Inch by inch, life's a cinch."
-from Harriet Zernickow, Abilene, Kansas (taken from Guideposts, November 2003 edition)
Another time it is attributed to UCLA Men's Basketball coach Steve Lavin (any Disney films about him?)
Several sites list it as a children's limerick/verse.
So I guess it could have been used in a Disney movie, but it's not a Disney original.