We are what we repeatedly do. Excellence, then, is not an act, but a habit.
—Aristotle

Stolen semi-shamelessly from Graybiel (2008) Annual Review of Neuroscience that has several fairly excellent habit quotes in the first page margin.

I feel compelled to note that this Graybiel review is not quite as awesomely titled as her 2005 review: “The basal ganglia: learning new tricks and loving it”