One of my favorites:
"Motivation is what gets you started, habit is what keeps you going."
Okay....here's another one:
"Your biggest challenge isn't someone else. It's the ache in your lungs, the burning in your legs and the voice inside you that yells "I CAN'T!" But you don't listen. You push harder. Then you hear that voice fade away and start to whimper "I can". That's the moment you discover that the person you thought you were is no match for the person you really are.
Your workouts are important meetings you schedule with yourself. Bosses don't cancel!
Don't give up what you want most for what you want now.
My new favourite motivational motto x
"We are what we repeatedly do. Excellence, then, is not an act, but a habit." – Aristotle
"When a man is sufficiently motivated, discipline will take care of itself." – Sir Alexander Paterson
"Two roads diverged in a wood, and I took the one less traveled by, and that has made all the difference." –Robert Frost
"Inspiration exists, but it must find you working." –Pablo Picasso