One of my favorite books is "Art & Fear" by David Bayle and Ted Orland.  I keep a copy in my nightstand and read it when I'm second-guessing myself in regards to my art.  I highly recommend it for all artists.  It is a small book and quick read.  Here is a quote from the book:

"The difference between art and craft lies not in the tools you hold in your hands, but in the mental set that guides them.  For the artisan, craft is an end in itself.  For you, the artist, craft is the vehicle for expressing your vision.  Craft is the visible edge of art."

Every artist should have this book.  It is really inexpensive (less than $10 on Amazon).  BUY IT!