Have you ever wanted to be a writer? You should be. You should sit down Sunday afternoon and begin writing the Great American Novel. It will be a smash hit, and you'll be remembered for generations. It'll probably be your grandchildren who get rich off the royalties when it becomes a classic, but you'll have made your contribution to posterity. It'll be satisfying.
The trouble for me is that if I set out to take pictures, nothing presents itself. With a million options before me, they seem too big, or too bright, or too boring (I rent movies at Redbox because they have three new releases; Blockbuster has too many choices). So, like writers, photographers give themselves mini assignments--a certain shape, a color, a number, groupings, signs, people, animals, etc. Bounds increase creativity.
Of course, it's even better when a customer makes the assignment for you.
Nikon D90, 50mm lens, f/3.5, 1/320s, ISO 200, two SB-600 speedlights fired through a 3x5 diffuser, background added. Inspired by Bruce Springsteen.