Mice and hamsters have an instinctual need to run whenever they can.
Their metabolism is fast, and they burn off energy almost as fast as they consume food. Fortunately too, mice are quick learners.
Curiosity leads them to the wheel to explore. Once on the wheel, it doesn’t take long for them to reach upward and roll a couple of times.
They soon learn that the wheel will move continuously, satisfying their need for physical activity.