A conical pendulum spins in one direction due to the initial torque applied when it is spun, which establishes a rotational motion. The forces acting on the pendulum, including tension and gravity, work together to maintain this circular path. If spun in the opposite direction, the pendulum does not travel in a circle because the forces would not align correctly to sustain that motion. The discussion emphasizes the importance of the initial spin direction in determining the pendulum's trajectory. Understanding these physics principles clarifies why the conical pendulum exhibits one-way motion.