If you miss one day you can miss two, if you miss two it's all over.
(which I wrote up here -- http://joshuaspodek.com/a-model-for-consistency)
Words to live by if you want consistency and discipline in your life.
I'm also coming up on two years without missing a single day of exercising, for which the same philosophy motivates me -- http://joshuaspodek.com/burpees-the-one-year-review
EDIT: Another lesson I learned: That the route to quality generally comes from quantity -- http://joshuaspodek.com/route-quality-quantity.