What unique perspective did the Apollo 8 crew, including Frank Borman, experience regarding Earth while orbiting the Moon?

They had their view of Earth entirely blocked by the Moon

The experience of the Apollo 8 astronauts was profoundly unique because, as they maneuvered into orbit around the Moon, they crossed the threshold where the solid body of the Moon completely obscured Earth from their vantage point. This moment represented the first time in human history that individuals were physically situated such that their view of the Earth was entirely occluded by another celestial body. This direct sensory experience emphasized the isolation and the unfamiliar nature of the far side landscape they were observing, contrasting sharply with all previous views where Earth remained a constant presence in the sky.