"The good is the enemy of the best." - anonymous quote I ran across this morning.
"The best is the enemy of the good." - Voltaire.
So which is it? It's probably both. In light of the first quote, we can never become so complacent that our way is "good enough." People and organizations must always strive to become better at whom they are and what they do. This is the center of continuous improvement and other process-centric improvement efforts. This idea is also the center of 3M and Google's efforts to set aside time for their employees to work on new (and different) ideas for products to help those organizations jump the boundaries of "we've always done it this way."
On the other hand, we don't want to spend so much time looking for the best that nothing happens. This is where I've heard the Voltaire quote used, particularly when railing against the idea of "best practices." The concern is that people and organizations spend so much time either trying to become the best or trying to find the best way to do something that they never actually get it done. As Hiebeler discussed at KMPro, there really are no true best practices, simply examples of best practices.