Victor's disrespect for the natural order of the world led to him learning how to create life after the death of his mother.
The event leading to Victor's downfall was his desire to put life into an inanimate object.
Victor's fortune turns when the monster starts killing the people he loved.
The important discovery Victor makes would be when the Monster tells him everything he did after his abandonment. Victor feels responsible for the Monster's actions.
After Victor loses every thing, he goes after the Monster to kill him. His unavoidable fate is that he dies trying to pursue the Monster with the intent of murder.
Victor's disrespect for the natural order of things and desire for fame led to the destruction of his family and himself. We learned from his experiences the consequences of too much ambition. We ultimately feel bad for him because he was not trying to create a monster in the beginning, he was just trying to create life.