The idea means that every natural phenomenon either has a reason for occurring (a cause) or seems to be directed toward a specific outcome (a final purpose). For example, a seed grows into a plant because it carries the potential (or built-in purpose) to mature, and nothing happens without some initiating factor. This observation leads to the thought that the universe operates under systematic, non-arbitrary principles, suggesting an underlying order that can be traced back to a first cause or prime mover.