We always see the same side of the Moon because the Moon is tidally locked to Earth. This means the Moon's rotation period on its axis is synchronized with its orbital period around Earth, both taking about 27.3 days. As a result, the same side of the Moon always faces Earth. This synchronous rotation is not a coincidence but the outcome of gravitational interaction over billions of years, where Earth's gravity slowed the Moon's initial faster rotation until it matched the orbital period. This phenomenon is known as tidal locking or synchronous rotation.
Although we say we only see one side, due to a subtle wobbling called lunar libration, slightly more than half (about 59%) of the Moon's surface can be seen from Earth over time.
In summary, the Moon's synchronous rotation with its orbit around Earth keeps one hemisphere constantly facing our planet, which is why we always see the same side.
