Ouroboros is symbol of the world snake, the snake that is curled around the universe. The snake is, in fact, a symbol of the universe constantly destroying and creating itself. By eating itself it grows and diminishes at the same moment. The process of destruction brings creation and everything that's created is destroyed. So: how can a system like the universe exist at all?
The same with nature as a whole. The paradoxical question of course is: How can nature exist by eating itself? You, the reader, must eat organic foods to stay alive and grow, and you too will be used as food for other organisms.