Elphaba, being green was not fit for the rich and high of society, nor the poor and lowly.

Galinda, being beautiful was the embodiment of high of society.

When Galinda went to a Slavery auction with her father at five, she saw something in the green monster that no one else did. When she begs her Popsicle to buy the seemingly deformed slave, she unknowingly started a series of events that would change both of their lives.