experience necessity

According to Hume, Descartes’s cosmological proof of the existence of God relied on a conceptual foundation that he had left unquestioned, the conceptual foundation of causality. Hume argues that if you really tried to build knowledge back up from the most basic elements of human nature (e.g., perception), then you could not claim that causality is something we can know to be true rather than something we can only believe to be true. Though we may see one event follow another, and see this sequence of events happen over and over again, it is impossible to see that this sequence of events must happen. In other words, we cannot experience necessity.

Gertz, Nolen. Nihilism (The MIT Press Essential Knowledge series), 19.

In the end, we are always free to act.