When someone says “Things Happen”, we think they are being superficial. That’s because we want to hear an explanation of why the thing has happened. In fact, the “Principle of Sufficient Reason” mandates that everything must have a reason or cause. Still, you can’t argue with the fact that things do happen.
Aristotle described four causes that explain why things happen. These four causes are called the efficient, material, formal, and final causes. This classification was all the rage back before the scientific revolution, but now it has been mostly abandoned. Still, with some modification, I believe it can be useful for the modern world.
Why do things happen? They happen by actions, from parts, into structures, and for functions.