The gravitational pull of the moon lifts up the ocean to cause tides. Well the Earth's gravitational pull is so strong on the moon that the heavier side of the moon always faces the Earth. This is called tidal locking. So the only way to ever see the far side of the moon is to go there. Humans have gone there before, but almost always during an Earth "full moon", which means the far side is unlit. We do have full images of the far side of the moon from remote probes, but the 21% of the far side that was lit had human eyes on it for the first time ever.