Quantum mechanics challenges conventional thinking by disputing classical notions of determinism and objective reality. Traditionally, physics assumed a world with definite properties independent of observation. Quantum mechanics, however, shows that phenomena like superposition, entanglement, and the observer effect imply that outcomes are probabilistic and that measurement plays a fundamental role in determining a system’s state. This upends the clear-cut separation between the observer and the observed, inviting philosophical reexamination of causality, reality, and our understanding of knowledge itself.