Krishna taught Bhagavad Gita to Arjuna during the Great War of Mahabharat. It helped Arjuna to overcome his despond and fight against Kouravas. Then he should have remained an enlightened person for life. But that didn't happen. After the war when his son Babruvaha approached him and requested him to consider him and his mother as family, Arjuna insulted him by saying that, "you must be the son of a prostitute since you are begging me to treat you as son. If you were my son you would have fought with me and asked me the same". My question is how and why did Arjuna forget the teachings of great Bhagavad Gita and behave with ego?