As far as I can tell, this quote is anonymous but is certainly one of my favorites.

How many times a day do you bargain with yourself, to avoid maximum effort? How often have you compromised somewhere between maximum potential and minimum daily requirements? That is just human nature you may say, but beware of a lurking danger! For it does not take long for the minimum to become the maximum that you are willing to do! When the minimum becomes your maximum, the sum of your life becomes mediocrity.  That is the way people for countless generations have lost a great portion of that character called “excellence.” All too often, we are willing to settle for a “comfort zone of mediocrity” caused by a diet of minimum commitment, minimum effort, minimum risk and minimum accomplishment in life.