It is understood from the creation of the sun and moon. They establish the paradigm that is later expressed via the creation of Adam and Chava. The sun shines on the moon, which then reflects the light received from the sun. The moon is a source of reflected light.
In the same way, Chava lost her direct memory of G-d's teachings when she was built from Adam HaRishon. At that point, she had to be taught by her husband what was expected of her. That's the main point of the sin of the Tree of Knowledge. Chava responded to the Nachash exactly what her husband had taught her. See Siftei Chachamim to Bereshit 3:2 beginning with the words, "כיון שהיא ידעה בעצמה כו׳" for details.