Photographers are notorious for being anal retentive. We like to control everything, especially our photography; we know exactly what time the sun is rising and setting, we know every specification of every lens, etc. And while that is fine, sometimes it’s good to allow yourself get side tracked.
Before going on any photo excursion you should try to plan ahead. Think through what kind of images you want to create, what the lighting conditions may be, what the potential problems are like, i.e. weather, and make sure you have the right equipment for the specific conditions. As most of us know, even with a lot of planning, things don’t always turn out the way we want them to; getting flustered and going home is often not an option, so then what? At this point you have to do the best you can and get your shot.
But what about times when things are going so well that you have nothing more to shoot? IN both of these situations, you should allow yourself to get side tracked. If you see something interesting even if it’s not what you originally intended to photograph, photograph it! Why not? You never know what you might find. Allow yourself to be spontaneous -- it’s important in life and in photography! Enjoy.