"Are we puppets of physics?"
Do you control your actions, or are they the inevitable result of prior causes? Determinism suggests that since the universe follows physical laws (cause and effect), and our brains are physical, every thought and action is pre-determined by the state of the universe before we were born.
We intuitively feel we are free. This view argues that humans have special agency—a soul or mind—that is not bound by physical causality. Without free will, moral responsibility seems impossible. How can we punish a criminal if he was 'destined' to commit the crime?
Many modern philosophers argue for a middle ground. Even if our desires are determined by biology and environment, as long as we act according to our desires without external coercion, we are 'free' in the only way that matters. We can be both determined and free.