An Event Has Many Causes
"Every Event Has A Cause" is a principle of universal causality so sweeping as to be of little practical use. Events have many contributing causes. Selecting the "one" cause of an event is an exercise in story-telling.

The ancient idea of a "causal chain," with one event being the cause of the next event, and so on ad infinitum, is a philosophical fiction.

Aristotle made it clear that there are many kinds of causes, classifying them as efficient, material, final, and formal. He also added accidental causes. His word for causes, aitia (ἀιτία), has as root meaning "the things responsible for" something.

Even in a simple mechanical and deterministic world like that of Pierre-Simon Laplace's "super-intelligence," the future motion of each particle is dependent on ("caused by") the positions, momenta, and forces of all the other particles in the world.

More sophisticated physical determinists refine their idea of determinism, including the notion of every event having a cause, to the idea that the state of the universe at time t is completely determined by the state of the world an instant earlier.

But because of quantum mechanics, we now know that indeterminism is true, irreducible chance exists in the universe, and there are many events that occur only probabilistically.

What this means is that tracing any particular sequence of events back in time will come to one event - a "starting point" or "fresh start" (Aristotle calls it an origin or arche (ἀρκῆ)) - whose major contributing cause (or causes) was itself uncaused, in that it involved quantum indeterminacy.

Whether a particular thing happens, says Aristotle, may depend on a series of causes that

"goes back to some starting-point, which does not go back to something else. This, therefore, will be the starting-point of the fortuitous, and nothing else is the cause of its generation."
Metaphysics Book VI 1027b12-14)

We can thus in principle assign times, or ages, to the starting points of the contributing causes of an event. Some of these may in fact go back before the birth of an agent, hereditary causes for example. To the extent that such causes adequately determine an action, we can understand why hard determinists think that the agent has no control over such actions. (Of course if we can opt out of the action at the last moment, we retain a kind of control.)

Other contributing causes may be traceable back to environmental and developmental events, perhaps education, perhaps simply life experiences, that were "character-forming" events. These and hereditary causes would be present in the mind of the agent as fixed habits, with a very high probability of "adequately determining" the agent's actions in many situations.

But other contributing causes of a specific action may have been undetermined up to the very near past, even seconds before an important decision. Most importantly, these will include the free generation of new alternative possibilities during the agent's deliberations.

Causes with these most recent starting points are the fundamental reason why an agent can do otherwise in what are essentially (up to that starting point) the same circumstances.

These alternatives are likely generated from our internal knowledge of practical possibilities based on our past experience. Those that are handed up for consideration may be filtered to some extent by unconscious processes to be "within reason." They may consist of slight variations of past actions we have willed many times in the past.

The evaluation and selection of one of these possibilities by the will is as deterministic and causal a process as anything that a determinist or compatibilist could ask for, consistent with our current knowledge of the physical world.

But remember that instead of strict causal determinism, the world offers only adequate determinism.

Just as determinism is limited, the role of random chance is limited. Rarely or never is chance the direct cause of action.

Consequently, in most cases the indeterminism or chance involved in the generation of alternative possibilities is just an indirect cause of action, and leads to just one of many contributing causes.

One of these possibilities is selected by our adequately determined will, so we can say that the action was up to us and that we can accept responsibility for it.

We might select something that we always do for hereditary reasons, of some habit that was formed by our education. But we always have the option of not doing those things, when our evaluation suggests good reasons for not doing them. And we may often select a brand new creative idea, one that has occurred to us only moments before we closed off deliberation and made our selection.

These new creative ideas originate within us (Aristotle's ἐν ἡμῖν.

If we extend the "moment of choice" backwards to include the deliberation process and its generation of new possibilities, we have captured the essence of an "agent-causal" liberty that is not necessitated by any particular past causes, but instead is the result of many contributing causes, some habitual with causal chains that go back before our deliberations, others distinctly lacking causal chains that go back before our deliberations and free generation of alternative possibilities.

The Cogito model explains not only human freedom but human creativity.

There is no causal chain back to the big bang
We can see that some causes may be traced back very far indeed. Instinctual acts, such as babies' sucking, or fight or flight reactions, may be traceable back to earlier ancestor species. But it is extremely improbable that the causal chains extend back to the prime mover or big bang of the universe, as some determinists believe.

Given the conservative nature of evolution, the fundamental strategy of random variation followed by lawful selection, a behavioral strategy present in the most primitive life forms (cf. Martin Heisenberg), may well be connected to our two-stage model of "free" possibilities followed by "willed" determinations in the higher animals and humans.

But although this ancient fundamental strategy may be present in human minds, its presence insures that the mind has access to randomness and a break with determinism when it needs it to create new alternative possibilities for totally unexpected situations, or importantly whenever the agent simply wants to be creative and original in thoughts or actions.

Since our decisions may always include options generated immediately before the decision, we can always "opt out" of an action at the very last moment, even if, before that moment, we were otherwise in exactly the same circumstances.
For Teachers
Stanford Encyclopedia of Philosophy
For Scholars
Aristotle Metaphysics VI iii describes the accidental starting points of new causal chains.
Clearly, then, the series goes back to some starting-point, which does not go back to something else. This, therefore, will be the starting-point of the fortuitous, and nothing else is the cause of its generation. But to what sort of starting-point and cause this process of tracing back leads, whether to a material or final or moving cause, is a question for careful consideration.

δῆλον ἄρα ὅτι μέχρι τινὸς βαδίζει ἀρχῆς, αὕτη δ᾽ οὐκέτι εἰς ἄλλο. ἔσται οὖν ἡ τοῦ ὁπότερ᾽ ἔτυχεν αὕτη, καὶ αἴτιον τῆς γενέσεως αὐτῆς ἄλλο οὐθέν. ἀλλ᾽ εἰς ἀρχὴν ποίαν καὶ αἴτιον ποῖον ἡ ἀναγωγὴ ἡ τοιαύτη, πότερον ὡς εἰς ὕλην ἢ ὡς εἰς τὸ οὗ ἕνεκα ἢ ὡς εἰς τὸ κινῆσαν, μάλιστα σκεπτέον.

Chapter 3.7 - The Ergod Chapter 4.2 - The History of Free Will
Part Three - Value Part Five - Problems