A client asked me this question recently: "What comes first in the design process, the floor plan or the outside of the house?"
Good question - the answer is a little complicated, and subjective, and contradictory...but doing it right can make the difference between good design and mediocre design.
I remember an interview with Elton John a few years ago, the interviewer wanted to know whether Elton wrote the music of his hit songs first, or if Bernie Taupin wrote the lyrics first. Elton said in almost every case, Bernie wrote the lyrics - then Elton put it to music with very little collaboration with Bernie.
Voila - mega hit song.