@Zenith: When you put the emphasis of the thought on excellence (or any other trait you could note there), it might make more sense to you 
Observe: Criminality, then, is not an act, but a habit.
Observe: Insanity, then, is not an act, but a habit.
That's the focus of his idea... though excellence as a habit does indeed partly define us.

Observe: Criminality, then, is not an act, but a habit.
Observe: Insanity, then, is not an act, but a habit.
That's the focus of his idea... though excellence as a habit does indeed partly define us.
Please give me a home where cloud buffalo roam
Where the dear and the strangers can play
Where sometimes is heard a discouraging word
But the skies are not stormy all day