...favorite athletic/motivational quotes (I'll add more)...

I think I've seen this on every other high school & college cross country shirt ever made...but it's still a good one:
"The woods are lovely, dark and deep.
But I have promises to keep,
And miles to go before I sleep,
And miles to go before I sleep."
- Robert Frost


I've seen several variations of this one, but the message is still the same:
"You can quit, and no one will care...but you will always know."
- Ironman founder, Cmdr. John Collins

Another Cmdr. John Collins gem:
On February 18, 1978 (first IM), 15 competitors, including Collins, came to the shores of Waikiki to take the Ironman challenge. Prior to racing, each received three sheets of paper listing a few rules and a course description. Handwritten on the last page was this exhortation:
“Swim 2.4 miles! Bike 112 miles! Run 26.2 miles! Brag for the rest of your life!”
- Ironman founder, Cmdr. John Collins

From John L. Parker's book, Once a runner:
"...trials of miles; miles of trials..."

First person to break 4 minutes for the mile:
"The man who can drive himself further once the effort gets painful is the man who will win."
- Sir Roger Bannister

From America's real pioneer in cycling:
"It never gets easier, you just go faster."
- Greg LeMond

"Somewhere in the world someone is training when you are not. When you race him, he will win."
- Tom Fleming's Boston Marathon Training Motto

Sounds like cross country to me:
"Most men take the straight and narrow. A few take the road less traveled. I chose to cut through the woods."
- Unknown

Amen:
"Americans have not had the same successes because of the fact that most grow up in the lap of luxury. They don't tolerate the type of pain that distance running demands. You can pass your Physical Education classes in school by walking a mile maybe twice a year. It seems that the few Americans who do make it on the international level have a tremendous drive and tolerance for discomfort. I think the main reason Africans succeed in distance running is many have to and we don't."
- Ryan Wilson

Famous University of Oregon coach (think Prefontaine), and cofounder of Nike:
"There's no such thing as bad weather, just soft people."
- Bill Bowerman