To know realities is to know the true nature of phenomena
We should remember that the Buddha in countless former lives as a Bodhisatta had to accumulate the "perfections"  ( generosity, morality, renunciation, wisdom, energy, patience, truthfulness, determination, loving kindness and equanimity ). In his last life during which he attained enlightenment, he was a human being, just like all of us. He was seeing visible object through the eyes, hearing sound through the ears and thinking of different things. However, he needed to know the true nature of seeing while he was seeing, he needed to know the true nature of hearing while he was hearing. He needed to know these phenomena as they are because they are realities. After seeing and hearing there are like and dislike of what had been seen and heard, and these are also realities which should be known as they are.
The Buddha knew that it is extremely difficult to know the true nature of phenomena such seeing or hearing, which are realties occuring time and again, in daily life. We could reduce our life to just one moment, because life actually occurs during one moment of citta which experiences an object and is then gone. However if one is not a Bodhisatta one is absorbed in thinking for a long time about what appears just for a moment through the eyes, the ears, the nose, the tongue, the bodysense or the mind. The Bodhisatta was altogether different from us who are time and again infatuated with what we experience. Since he knew that the way leading to enlightenment was extremely difficult, he accumulated patience, energy and the other perfections, which were necessary conditons to attain Buddhahood. He had endless endurance and he did not become disheartened while he accumulated the perfections with the purpose to penetrate the truth of realities and to be able to teach other beings, so that they also could become free from dukkha just like he himself    

Topic 80