Painting a Series

I have a thing for series.  I love to read books in a series and I love to paint in a series. There is a deeper connection to the subject matter than there is when you just take one swipe at it...
The first painting in a series is generally the most  labored and careful.  The second painting I've loosened up and explored some creative deviations from what I originally intended.  The third painting is usually the best- it's free of thought process constraints.  Why can't I just start out with painting #3?  Like my paintings, I am a work in progress.  Oh, and by the way, I very rarely paint #4.  I also have a short attention span- by the time I've reached #4 I'm bored!