Most (many) photographers concentrate on one theme area…landscape, nature, birds, theater, and so forth. But the truth is a photographer must branch out if for nothing else than honing his or her skills.  Although my main concentration is landscape, I sometimes photograph ballet, birds or still-life to sharpen equipment and lightingskills.  Birds can be a test of your reflexes, focusing skills, and concentration, while ballet forces you to think about low light and the accompanying noise in an image taken at ISO 5000.  Just a though.