Rules, of course, are meant to be broken. The rule of symmetry is all about capturing the natural symmetry in nature. There are a few ways to do this. You might shoot a scene in which both sides of your photo are essentially the same, for example. Or you might shoot a photo of something that is itself quite symmetrical, like a flower.
Even better, though, is when you incorporate a lesson from the rule about monotonous content and shake things up with a little variation. Surprise the viewer, either by making one side of the photo non-symmetrical, or, in this example, defeat the symmetry of the flower by shooting only part of it in the frame.